Siiyama (serine 53 (TCC) to phenylalanine 53 (TTC)). A new alpha 1-antitrypsin-deficient variant with mutation on a predicted conserved residue of the serpin backbone

Pulmonary manifestations of alpha 1 antitrypsin deficiency

Alpha 1 antitrypsin deficiency is a widely under recognized autosomal codominant condition caused by genetic mutations in the SERPINA 1 gene, which encodes for alpha 1 antitrypsin (AAT), a serine protease inhibitor. The SERPINA 1 gene contains 120 variants and mutations in the gene may decrease AAT protein levels or result in dysfunctional proteins. This deficiency leads to unopposed protease activity in tissues, thereby promoting pulmonary and hepatic disease. The most common genotype associated with pulmonary disease is the ZZ genotype, and the most frequent pulmonary manifestation is emphysema. Although its pathophysiology may differ from cigarette smoking related chronic obstructive pulmonary disease, smoking itself can hasten lung decline in alpha 1 antitrypsin deficiency (AATD). The diagnosis of AATD is made through AAT protein testing along with genotyping. AATD patients with obstructive airflow limitation may qualify for intravenous augmentation with AAT. However, there is ongoing research to allow for earlier detection and treatment. This review describes in general terms the genetic mechanisms of AATD; its pathogenesis and the impact of cigarette smoke; and its clinical manifestations, diagnosis, treatment, and prognosis. We hope to stimulate research in the field, but mostly we wish to enhance awareness to promote early diagnosis and treatment in those eligible for intervention.

ER chaperones use a protein folding and quality control glyco-code

N-glycans act as quality control tags by recruiting lectin chaperones to assist protein maturation in the endoplasmic reticulum. The location and composition of N-glycans (glyco-code) are key to the chaperone-selection process. Serpins, a class of serine protease inhibitors, fold non-sequentially to achieve metastable active states. Here, the role of the glyco-code in assuring successful maturation and quality control of two human serpins, alpha-1 antitrypsin (AAT) and antithrombin III (ATIII), is described. We find that AAT, which has glycans near its N terminus, is assisted by early lectin chaperone binding. In contrast, ATIII, which has more C-terminal glycans, is initially helped by BiP and then later by lectin chaperones mediated by UGGT reglucosylation. UGGT action is increased for misfolding-prone disease variants, and these clients are preferentially glucosylated on their most C-terminal glycan. Our study illustrates how serpins utilize N-glycan presence, position, and composition to direct their proper folding, quality control, and trafficking.

Distribution of alpha1 antitrypsin rare alleles in six countries: Results from the Progenika diagnostic network

BACKGROUND

Knowledge of the frequency of rare SERPINA1 mutations could help in the management of alpha1 antitrypsin deficiency (AATD). The present study aims to assess the frequencies of rare and null alleles and their respiratory and hepatic pathogenicity.

METHODS

This is a secondary analysis of a study that evaluated the viability of the Progenika diagnostic genotyping system in six different countries by analyzing 30,827 samples from cases of suspected AATD. Allele-specific genotyping was carried out with the Progenika A1AT Genotyping Test which analyses 14 mutations in buccal swabs or dried blood spots samples. SERPINA1 gene sequencing was performed for serum AAT-genotype discrepancies or by request of the clinician. Only cases with rare mutations were included in this analysis.

RESULTS

There were 818 cases (2.6%) carrying a rare allele, excluding newly identified mutations. All were heterozygous except for 20 that were homozygous. The most frequent alleles were the M-like alleles, PI*M_malton and PI*M_heerlen. Of the 14 mutations included in the Progenika panel, there were no cases detected of PI*S_iiyama, PI*Q0_{granite falls} and PI*Q0_west. Other alleles not included in the 14-mutation panel and identified by gene sequencing included PI*M_würzburg, PI*Z_bristol, and PI*Z_wrexham, and the null alleles PI*Q0_porto, PI*Q0_madrid, PI*Q0_brescia, and PI*Q0_kayseri.

CONCLUSIONS

The Progenika diagnostic network has allowed the identification of several rare alleles, some unexpected and not included in the initial diagnostic panel. This establishes a new perspective on the distribution of these alleles in different countries. These findings may help prioritize allele selection for routine testing and highlights the need for further research into their pathogenetic role.

The conformational landscape of a serpin N-terminal subdomain facilitates folding and in-cell quality control

Many multi-domain proteins including the serpin family of serine protease inhibitors contain non-sequential domains composed of regions that are far apart in sequence. Because proteins are translated vectorially from N- to C-terminus, such domains pose a particular challenge: how to balance the conformational lability necessary to form productive interactions between early and late translated regions while avoiding aggregation. This balance is mediated by the protein sequence properties and the interactions of the folding protein with the cellular quality control machinery. For serpins, particularly α 1 -antitrypsin (AAT), mutations often lead to polymer accumulation in cells and consequent disease suggesting that the lability/aggregation balance is especially precarious. Therefore, we investigated the properties of progressively longer AAT N-terminal fragments in solution and in cells. The N-terminal subdomain, residues 1-190 (AAT190), is monomeric in solution and efficiently degraded in cells. More β -rich fragments, 1-290 and 1-323, form small oligomers in solution, but are still efficiently degraded, and even the polymerization promoting Siiyama (S53F) mutation did not significantly affect fragment degradation. In vitro, the AAT190 region is among the last regions incorporated into the final structure. Hydrogen-deuterium exchange mass spectrometry and enhanced sampling molecular dynamics simulations show that AAT190 has a broad, dynamic conformational ensemble that helps protect one particularly aggregation prone β -strand from solvent. These AAT190 dynamics result in transient exposure of sequences that are buried in folded, full-length AAT, which may provide important recognition sites for the cellular quality control machinery and facilitate degradation and, under favorable conditions, reduce the likelihood of polymerization.

Known Mutations at the Cause of Alpha-1 Antitrypsin Deficiency an Updated Overview of SERPINA1 Variation Spectrum

Alpha-1-Antitrypsin deficiency (AATD), caused by SERPINA1 mutations, is one of the most prevalent Mendelian disorders among individuals of European descend. However, this condition, which is characterized by reduced serum levels of alpha-1-antitrypsin (AAT) and associated with increased risks of pulmonary emphysema and liver disease in both children and adults, remains frequently underdiagnosed. AATD clinical manifestations are often correlated with two pathogenic variants, the Z allele (p.Glu342Lys) and the S allele (p.Glu264Val), which can be combined in severe ZZ or moderate SZ risk genotypes. Yet, screenings of AATD cases and large sequencing efforts carried out in both control and disease populations are disclosing outstanding numbers of rare SERPINA1 variants (>500), including many pathogenic and other likely deleterious mutations. Generally speaking, pathogenic variants can be subdivided into either loss- or gain-of-function according to their pathophysiological effects. In AATD, the loss-of-function is correlated with an uncontrolled activity of elastase by its natural inhibitor, the AAT. This phenomenon can result from the absence of circulating AAT (null alleles), poor AAT secretion from hepatocytes (deficiency alleles) or even from a modified inhibitory activity (dysfunctional alleles). On the other hand, the gain-of-function is connected with the formation of AAT polymers and their switching on of cellular stress and inflammatory responses (deficiency alleles). Less frequently, the gain-of-function is related to a modified protease affinity (dysfunctional alleles). Here, we revisit SERPINA1 mutation spectrum, its origins and population history with a greater emphasis on variants fitting the aforementioned processes of AATD pathogenesis. Those were selected based on their clinical significance and wider geographic distribution. Moreover, we also provide some directions for future studies of AATD clinically heterogeneity and comprehensive diagnosis.

The Discovery of Endoplasmic Reticulum Storage Disease. The Connection between an H&E Slide and the Brain

The revolutionary evolution in science and technology over the last few decades has made it possible to face more adequately three main challenges of modern medicine: changes in old diseases, the appearance of new diseases, and diseases that are unknown (mostly genetic), despite research efforts. In this paper we review the road travelled by pathologists in search of a method based upon the use of routine instruments and techniques which once were available for research only. The application to tissue studies of techniques from immunology, molecular biology, and genetics has allowed dynamic interpretations of biological phenomena with special regard to gene regulation and expression. That implies stepwise investigations, including light microscopy, immunohistochemistry, in situ hybridization, electron microscopy, molecular histopathology, protein crystallography, and gene sequencing, in order to progress from suggestive features detectable in routinely stained preparations to more characteristic, specific, and finally, pathognomonic features. Hematoxylin and Eosin (H&E)-stained preparations and appropriate immunohistochemical stains have enabled the recognition of phenotypic changes which may reflect genotypic alterations. That has been the case with hepatocytic inclusions detected in H&E-stained preparations, which appeared to correspond to secretory proteins that, due to genetic mutations, were retained within the rough endoplasmic reticulum (RER) and were deficient in plasma. The identification of this phenomenon affecting the molecules alpha-1-antitrypsin and fibrinogen has led to the discovery of a new field of cell organelle pathology, endoplasmic reticulum storage disease(s) (ERSD). Over fifty years, pathologists have wandered through a dark forest of complicated molecules with strange conformations, and by detailed observations in simple histopathological sections, accompanied by a growing background of molecular techniques and revelations, have been able to recognize and identify arrays of grotesque polypeptide arrangements.

Changes in strand 6B and helix B during neuroserpin inhibition: Implication in severity of clinical phenotype

Neuroserpin (NS) is predominantly expressed in brain and inhibits tissue-type plasminogen activator (tPA) with implications in brain development and memory. Nature of conformational change in pathological variants in strand 6B and helix B of NS that cause a relatively mild to severe epilepsy (and/or dementia) remains largely elusive. MD simulation with wild type (WT) NS, strand 6B and helix B variants indicated that substitution in this region affects the conformation of the strands 5B, 5A and reactive centre loop. Therefore, we designed variants of NS in strand 6B (I46D and F48S) and helix B (A54F, L55A and L55P) to investigate their role in tPA inhibition mechanism and propensity to aggregate. An interaction analysis showed disturbance of a hydrophobic patch centered at strands 5B, 6B and helix B in I46D and F48S but not in A54F, L55A, L55P and WT NS. Purified I46D, F48S and L55P variants showed decrease in fluorescence emission intensity but have similar α-helical content, however results of A54F and L55A were comparable to WT NS. Analysis of tPA inhibition showed marginal effect on A54F and L55A variant with tPA-NS complex formation. In contrast, I46D, F48S and L55P variants showed massive decrease in tPA inhibition, with no tPA-NS complex formation. Analysis of native PAGE under under polymerization condition showed prompt conversion of I46D, F48S and L55P to latent conformation but not A54F and L55A variants. Identification of these novel conformational changes will aid in the understanding of variable clinical phenotype of shutter region NS variants and other serpins.

Functional characterization of a SNP (F51S) found in human alpha 1-antitrypsin

BACKGROUND

Alpha 1-antitrypsin (A1AT) deficiency is related to lung and liver diseases, including pulmonary emphysema and liver cirrhosis in humans. Genetic variations including single nucleotide polymorphisms (SNPs) of SERPINA1 are responsible for A1AT deficiency, but the characteristics of the SNPs are not well-understood. Here, we investigated the features of a rare SNP (F51S) of A1AT, which introduces an additional N-glycosylation site in the N-terminal region of A1AT.

METHODS

We evaluated the F51S variant compared with the wild-type (WT) A1AT with regard to expression in CHO-K1 cells, trypsin inhibitory activity, polymerization, and thermal stability.

RESULTS

The recombinant F51S protein expressed in CHO-K1 cells was mostly retained inside cells. The F51S variant had trypsin inhibitory activity, but reduced thermal stability compared with the WT A1AT. The native acrylamide gel data showed that F51S tended to prevent polymerization of A1AT.

CONCLUSION

The results of this study indicate that Phe51 and the surrounding hydrophobic residue cluster plays an important role in the conformation and secretion of A1AT and suggest the harmful effects of a rare F51S SNP in human health.

Safety and pharmacokinetics of Alpha-1 MP (Prolastin®-C) in Japanese patients with alpha1-antitrypsin (AAT) deficiency

BACKGROUND

Alpha₁-Proteinase Inhibitor, Modified Process (Alpha-1 MP) is used for augmentation therapy in alpha1-antitrypsin deficiency (AATD), an extremely rare disease in Japan. Weekly doses of 60 mg/kg Alpha-1 MP have been shown to be safe and well tolerated in non-Japanese subjects, but the safety and pharmacokinetics (PK) have not been evaluated in Japanese subjects. The objectives of this study were to evaluate the safety and PK of 60 mg/kg Alpha-1 MP administered by weekly IV infusions over 8 weeks in Japanese subjects with AATD.

METHODS

This was a multicenter, open-label trial in Japanese adults aged ≥20 years with AATD. Samples for evaluation of serum alpha₁-PI concentration and PK parameters were collected at 10 time points until the seventh day after the last dose at Week 8: immediately before dosing, immediately after dosing (time 0), and 0.25, 2, 4, 8, 24, 48, 120, and 168 hours after dosing.

RESULTS

Four subjects were analyzed. The median t_max was 0.534 h. Mean ± SD values for t_½, C_max, and AUC_0-7days were 150.4 ± 36.18 h, 174.2 ± 30.51 mg/dL, and 14,913.2 ± 1633.45 mg*h/dL, respectively. Mean trough concentration at week 8 was 55.4 ± 7.23 mg/dL. Alpha-1 MP therapy was safe, with no serious adverse events or deaths reported. Two treatment-emergent adverse events of fatigue in one subject were considered to be possibly related.

CONCLUSIONS

The PK and safety of Alpha-1 MP in Japanese subjects with AATD were consistent with the Alpha-1 MP profile in non-Japanese subjects (ClinicalTrials.gov: NCT02870309; JAPIC CTI: JapicCTI-163160).

Oxidation-resistant and thermostable forms of alpha-1 antitrypsin from Escherichia coli inclusion bodies

Native α1‐antitrypsin (AAT) is a 52‐kDa glycoprotein that acts as an antiprotease and is the physiological inhibitor of neutrophil serine proteases. The main function of AAT is to protect the lung from proteolytic damage induced by inflammation. AAT deficiency (AATD) is a codominant autosomal disorder caused by pathogenic mutations in SERPINA1 gene, leading to reduced levels of serum AAT. The deficiency is known to increase the risk of pulmonary emphysema and chronic obstructive pulmonary disease as a consequence of proteolytic imbalance induced by inflammation, associated in many instances with cigarette smoking and other environmental hazards. Currently, the available therapy for lung disease associated with AATD is serum purified human AAT injected into patients on a weekly basis. It would be advantageous to replace serum‐derived AAT with a recombinant version which is stable and resistant to oxidation. We have expressed AAT in Escherichia coli as inclusion bodies and developed a highly efficient refolding and purification process. We engineered a series of mutant forms of AAT to achieve enhance thermostability and oxidation resistance. Moreover, we synthesized an active form of AAT via cysteine‐pegylation to achieve a markedly extended half‐life in vivo. The resulting molecule, which retains comparable activity to the wild‐type form, is expected to be an improved therapeutic agent for treating hereditary emphysema. In addition, the molecule may also be used to treat other types of emphysema caused by smoking, cystic fibrosis, pulmonary hypertension, pulmonary fibrosis, and chronic obstructive pulmonary disease.

α1-Antitrypsin Deficiency

α1-Antitrypsin deficiency is an autosomal codominant condition that predisposes to emphysema and cirrhosis. The condition is common but grossly under-recognized. Identifying patients' α1-antitrypsin deficiency has important management implications (ie, smoking cessation, genetic and occupational counseling, and specific treatment with the infusion of pooled human plasma α1-antitrypsin). The weight of evidence suggests that augmentation therapy slows the progression of emphysema in individuals with severe α1-antitrypsin deficiency.

Deficient and Null Variants of SERPINA1 Are Proteotoxic in a Caenorhabditis elegans Model of α1-Antitrypsin Deficiency

α1-antitrypsin deficiency (ATD) predisposes patients to both loss-of-function (emphysema) and gain-of-function (liver cirrhosis) phenotypes depending on the type of mutation. Although the Z mutation (ATZ) is the most prevalent cause of ATD, >120 mutant alleles have been identified. In general, these mutations are classified as deficient (<20% normal plasma levels) or null (<1% normal levels) alleles. The deficient alleles, like ATZ, misfold in the ER where they accumulate as toxic monomers, oligomers and aggregates. Thus, deficient alleles may predispose to both gain- and loss-of-function phenotypes. Null variants, if translated, typically yield truncated proteins that are efficiently degraded after being transiently retained in the ER. Clinically, null alleles are only associated with the loss-of-function phenotype. We recently developed a C. elegans model of ATD in order to further elucidate the mechanisms of proteotoxicity (gain-of-function phenotype) induced by the aggregation-prone deficient allele, ATZ. The goal of this study was to use this C. elegans model to determine whether different types of deficient and null alleles, which differentially affect polymerization and secretion rates, correlated to any extent with proteotoxicity. Animals expressing the deficient alleles, Mmalton, Siiyama and S (ATS), showed overall toxicity comparable to that observed in patients. Interestingly, Siiyama expressing animals had smaller intracellular inclusions than ATZ yet appeared to have a greater negative effect on animal fitness. Surprisingly, the null mutants, although efficiently degraded, showed a relatively mild gain-of-function proteotoxic phenotype. However, since null variant proteins are degraded differently and do not appear to accumulate, their mechanism of proteotoxicity is likely to be different to that of polymerizing, deficient mutants. Taken together, these studies showed that C. elegans is an inexpensive tool to assess the proteotoxicity of different AT variants using a transgenic approach.

Clinical heterogeneity and potential high pathogenicity of the Mmalton Alpha 1 antitrypsin allele at the homozygous, compound heterozygous and heterozygous states

Background

Alpha 1 antitrypsin (A1AT) deficiency (A1ATD) is potentially associated with a high degree of liver and/or lung disease. Apart from the most frequent deficiency alleles, Pi S and Pi Z, some A1AT alleles of clinical significance may be easily misdiagnosed. This is typically the case of the Pi Mmalton variant which shares the same ‘gain-of-function’ liver toxicity than Pi Z and the same ‘loss of function’ lung disease as well.

Methods

The biological diagnosis of A1ATD typically relies on a low serum concentration associated with an abnormal isoelectric focusing (IEF) pattern of migration. However, Sanger direct DNA sequencing may be required for deficiency alleles without biochemical expression (Null alleles) or for A1AT variants whose IEF profiles resemble the wild-type and sub-types M allele but with a low concentration.

Results

We report four cases of A1ATD involving the deficient Pi Mmalton allele with very different clinical expressions: (i) one Mmalton/Mmalton with liver fibrosis and cirrhosis, (ii) two Mmalton/Z with chronic pulmonary obstructive disease in one case and (iii) one M/Mmalton without liver or lung disease. In both cases, the correct diagnosis has necessitated a genetic analysis.

Conclusions

Our study provides another example of Pi Mmalton homozygosity associated with a severe liver disease that emphasizes the necessity of a not delayed diagnosis. The great clinical heterogeneity of the other genotypes (which is in agreement with the literature data) questions about the role of environmental and other modifier genes in the pathogenicity of A1ATD.

High-throughput screening of tumor metastatic-related differential glycoprotein in hepatocellular carcinoma by iTRAQ combines lectin-related techniques

Glycoproteomics is an important aspect in the research of cancer biomarker discovery. The objective of our study is to screen the profile of serum glycoproteins in hepatocellular carcinoma (HCC) patients and to discover differentially expressed glycoproteins in HCC with or without metastasis. We collected serum from HCC patients and divided them into two groups (non-metastatic HCC group and metastatic HCC group) according to 2002 UICC TNM staging system. Wheat germ agglutinin (WGA) lectin was used to enrich the serum glycoproteins by lectin affinity chromatography. The enriched glycoproteins were labeled with mass-balanced isobaric tags (iTRAQ) and analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Two differential glycoproteins were validated by Western blot and biochemical methods, respectively. Fifteen differential serum glycoproteins with WGA affinity were identified (p < 0.05). Among them, nine proteins were up-regulated (>1.5-folds) and six were down-regulated (<0.5-folds) in HCC patients with metastasis. Expression of alpha-1-antitrypsin (SERPINA1) and apolipoprotein A-I (APOA1) was validated by Western blot and biochemical methods, respectively (p < 0.05). Our study has obtained a set of HCC metastasis-associated glycoproteins which may serve as novel prognostic candidates and potential therapeutic targets for HCC metastasis. SERPINA1 might act as a potential glycoprotein biomarker of HCC metastasis.

Identification of compound heterozygous mutation in a Korean patient with alpha 1-antitrypsin deficiency

Alpha 1-antitrypsin (AAT) deficiency is a genetic disorder that primarily affects the lungs and liver. While AAT deficiency is one of the most common genetic disorders in the Caucasian population, it is extremely rare in Asians. Here, we report the case of a 36-year-old Korean woman with AAT deficiency who visited the emergency department of our hospital for the treatment of progressive dyspnea that had begun 10 years ago. She had never smoked. Chest computed tomography revealed panlobular emphysema in both lungs, which suggested AAT deficiency. The serum AAT level was 33 mg/dL (reference interval: 90-200 mg/dL). Four exons of the SERPINA1 gene, which is responsible for AAT deficiency, and their flanking regions were analyzed by PCR-direct sequencing. The patient was found to have 1 missense mutation (c.230C>T, p.Ser77Phe; S_iiyama) and 1 frameshift mutation (c.1158dupC, p.Glu387ArgfsX14; QO_clayton). This is the first Korean case of AAT deficiency confirmed by genetic analysis and the second case of a compound heterozygote of S_iiyama and QO_clayton, the first case of which was reported from Japan.

The discovery of α1-antitrypsin and its role in health and disease

α1-Antitrypsin (AAT) is the archetype member of the serine protease inhibitor (SERPIN) supergene family. The AAT deficiency is most often associated with the Z mutation, which results in abnormal Z AAT folding in the endoplasmic reticulum of hepatocytes during biogenesis. This causes intra-cellular retention of the AAT protein rather than efficient secretion with consequent deficiency of circulating AAT. The reduced serum levels of AAT contribute to the development of chronic obstructive pulmonary disease (COPD) and the accumulation of abnormally folded AAT protein increases risk for liver diseases. In this review we show that with the discovery of AAT deficiency in the early 60s as a genetically determined predisposition to the development of early-onset emphysema, intensive investigations of enzymatic mechanisms that produce lung destruction in COPD were pursued. To date, the role of AAT in other than lung and liver diseases has not been extensively examined. Current findings provide new evidence that, in addition to protease inhibition, AAT expresses anti-inflammatory, immunomodulatory and antimicrobial properties, and highlight the importance of this protein in health and diseases. In this review co-occurrence of several diseases with AAT deficiency is discussed.

α1-Antitrypsin deficiency, chronic obstructive pulmonary disease and the serpinopathies

α1-Antitrypsin is the prototypical member of the serine proteinase inhibitor or serpin superfamily of proteins. The family includes α1-antichymotrypsin, C1 inhibitor, antithrombin and neuroserpin, which are all linked by a common molecular structure and the same suicidal mechanism for inhibiting their target enzymes. Point mutations result in an aberrant conformational transition and the formation of polymers that are retained within the cell of synthesis. The intracellular accumulation of polymers of mutant α1-antitrypsin and neuroserpin results in a toxic gain-of-function phenotype associated with cirrhosis and dementia respectively. The lack of important inhibitors results in overactivity of proteolytic cascades and diseases such as COPD (chronic obstructive pulmonary disease) (α1-antitrypsin and α1-antichymotrypsin), thrombosis (antithrombin) and angio-oedema (C1 inhibitor). We have grouped these conditions that share the same underlying disease mechanism together as the serpinopathies. In the present review, the molecular and pathophysiological basis of α1-antitrypsin deficiency and other serpinopathies are considered, and we show how understanding this unusual mechanism of disease has resulted in the development of novel therapeutic strategies.

Mutation-, aging-, and gene dosage-dependent accumulation of neuroserpin (G392E) in endoplasmic reticula and lysosomes of neurons in transgenic mice

Mutations in human neuroserpin gene cause an autosomal dementia, familial encephalopathy with neuroserpin inclusion bodies (FENIB). We generated and analyzed transgenic mice expressing high levels of either FENIB-type (G392E) or wild-type human neuroserpin in neurons of the central nervous system. G392E neuroserpin accumulated age-dependently in neurons of the neocortex, thalamus, amygdala, pons, and spinal cord of homozygous transgenic mice. Such accumulations were not observed in hemizygous transgenic mice nor in transgenic mice for wild-type neuroserpin. In differential centrifugation of brain homogenates, G392E neuroserpin recovered in the nucleus-rich fraction dramatically increased along with aging, suggesting that the aggregations gradually increase their densities presumably by their conversion into heavier and more compact configurations. In immunoelectron microscopical analyses, immunopositivities for G392E neuroserpin were found not only in endoplasmic reticulum but also in lysosomes. G392E neuroserpin transgenic mice were much more susceptible to seizures induced by kainate administration than nontransgenic mice. Overall, G392E neuroserpin accumulated in the central nervous system neurons of transgenic mice in mutation-, aging-, and gene dosage-dependent manners. The established transgenic mice will be valuable to elucidate not only mechanisms for the formation of G392E neuroserpin aggregations but also pathways for the degradation and/or clearance of the already formed aggregations in neurons.

Alpha one antitrypsin deficiency: from gene to treatment

Alpha1-antitrypsin deficiency is a genetic disorder which contributes to the development of chronic obstructive pulmonary disease, bronchiectasis, liver cirrhosis and panniculitis. The discovery of alpha1-antitrypsin and its function as an antiprotease led to the protease-antiprotease hypothesis, which goes some way to explaining the pathogenesis of emphysema. This article will review the clinical features of alpha1-antitrypsin deficiency, the genetic mutations known to cause it, and how they do so at a molecular level. Specific treatments for the disorder based on this knowledge will be reviewed, including alpha1-antitrypsin replacement, gene therapy and possible future therapies, such as those based on stem cells.

Protein misfolding and the serpinopathies

The serpins are the largest superfamily of protease inhibitors. They are found in almost all branches of life including viruses, prokaryotes and eukaryotes. They inhibit their target protease by a unique mechanism that involves a large conformational transition and the translocation of the enzyme from the upper to the lower pole of the protein. This complex mechanism, and the involvement of serpins in important biological regulatory processes, makes them prone to mutation-related diseases. For example the polymerization of mutant alpha(1)-antitrypsin leads to the accumulation of ordered polymers within the endoplasmic reticulum of hepatocytes in association with cirrhosis. An identical process in the neuron specific serpin, neuroserpin, results in the accumulation of polymers in neurons and the dementia FENIB. In both cases there is a clear correlation between the molecular instability, the rate of polymer formation and the severity of disease. A similar process underlies the hepatic retention and plasma deficiency of antithrombin, C1 inhibitor, alpha(1)-antichymotrypsin and heparin co-factor II. The common mechanism of polymerization has allowed us to group these conditions together as a novel class of disease, the serpinopathies.

Alpha-antitrypsin genotypes in Korean patients with chronic obstructive pulmonary disease

OBJECTIVE

Alpha1-antitrypsin (AAT) deficiency is a recognized susceptible factor for chronic obstructive pulmonary disease (COPD) in Western countries, but its importance in Korea is unclear. To date, no definitive case of alpha1-antitrypsin deficiency has been reported in Korea. This study aimed to clarify whether alpha1-antitrypsin deficiency exists and to determine the distribution of alpha1-antitrypsin alleles in the Korean population.

METHODOLOGY

The serum concentrations of alpha1-antitrypsin were determined and polymorphisms of the alpha1-antitrypsin gene in 114 COPD patients and in 196 healthy controls were examined. Phenotyping by isoelectric focusing and the genotyping of alpha1-antitrypsin gene by polymerase chain reaction and restriction fragment length polymorphism were performed.

RESULTS

No alpha1-antitrypsin level abnormality was found in the patients. M1(Val)/M1(Val) was found to be the most frequent genotype in both groups (69.2% and 66.8%, respectively), and M1(Val) the most frequent allele. The distributions of alpha1-antitrypsin alleles were similar in the patient and control groups, and no S or Z allele was found.

CONCLUSION

Alpha1-antitrypsin deficiency is unlikely to be an important cause of chronic obstructive pulmonary disease in the Korean population.

Alpha-1-antitrypsin associated panniculitis: the MS variant

Over 90 mutant alleles of the alpha-1-antitrypsin (AAT) gene are recognized and classified by mobility on an acid starch gel. The four major categories include: F=fast, M=medium, S=slow, Z=very slow. Among 41 reported cases of AAT panniculitis, most have the ZZ phenotype with AAT levels below normal. We report two cases of AAT panniculitis with MS phenotype and normal AAT levels. In addition, we review the pathophysiology, epidemiology, and extracutaneous manifestations of AAT disease and propose a diagnostic algorithm for ulcerative panniculitis. A 42-year-old man presented with a solitary plaque on the left thigh exacerbated by trauma or excessive activity. The lesion frequently suppurated with a yellowish oily material. Twenty years before, he had fractured his left femur which was repaired with a metal plate. X-rays, histology with special stains for organisms, and cultures were negative. AAT phenotype was MS and AAT value was normal. A 43-year-old woman presented with multiple plaques on the proximal extremities which suppurated with exercise or trauma. AAT phenotype was MS and AAT level was normal. Histologic exam for both patients showed a dense neutrophilic infiltrate with septal and lobular panniculitis and areas of necrobiosis in the lower reticular dermis.

Comparison of the properties of rare variants of alpha1-proteinase inhibitor expressed in COS-1 cells and assessment of their potential as risk factors in human disease

Among the more than 75 known variants of alpha(1)-proteinase inhibitor, a sub-population of rare, point mutations causing single amino acid replacements have been identified and classified as "at risk" alleles for development of pulmonary disease. In most cases, it is not clear how the amino acid replacements typical of these variants change the properties of the inhibitor to increase risk of disease in the affected individuals. To begin to address this question, we mutagenized a wild type alpha(1)-proteinase inhibitor cDNA to encode a panel of eight different point mutants reported to be associated with increased risk for development of pulmonary disease. These variants were then expressed in COS-l cells transiently transfected with plasmids containing the altered cDNAs. The effects of the mutations on the rates of secretion, cellular location, intracellular degradation, activity, stability, and tendency to aggregate were determined. Results of these studies show that, in some cases, the mutations affect the rate of secretion, the activity or both of these properties of alpha(1)-proteinase inhibitor in a manner consistent with its designation as an "at-risk" allele. In other cases, the mutations do not significantly change the properties of the inhibitor, suggesting that these may be normal variants and that their expression may not increase the risk of disease.

Molecular mousetraps and the serpinopathies1

Members of the serine proteinase inhibitor or serpin superfamily inhibit their target proteinases by a remarkable conformational transition that involves the enzyme being translocated more than 70 Å (1 Å=10−10 m) from the upper to the lower pole of the inhibitor. This elegant mechanism is subverted by point mutations to form ordered polymers that are retained within the endoplasmic reticulum of secretory cells. The accumulation of polymers underlies the retention of mutants of α1-antitrypsin and neuroserpin within hepatocytes and neurons to cause cirrhosis and dementia respectively. The formation of polymers results in the failure to secrete mutants of other members of the serpin superfamily: antithrombin, C1 inhibitor and α1-antichymotrypsin, to cause a plasma deficiency that results in the clinical syndromes of thrombosis, angio-oedema and emphysema respectively. Understanding the common mechanism underlying the retention and deficiency of mutants of the serpins has allowed us to group these conditions as the serpinopathies. We review in this paper the molecular and structural basis of the serpinopathies and show how this has allowed the development of specific agents to block the polymerization that underlies disease.

Differential detection of PAS-positive inclusions formed by the Z, Siiyama, and Mmalton variants of alpha1-antitrypsin

Several point mutations of alpha(1)-antitrypsin cause a perturbation in protein structure with consequent polymerization and intracellular accumulation. The retention of polymers of alpha(1)-antitrypsin within hepatocytes results in protein overload that in turn is associated with juvenile hepatitis, cirrhosis, and hepatocellular carcinoma. The detection of alpha(1)-antitrypsin polymers and understanding the molecular basis of polymer formation is of considerable clinical importance. We have used a monoclonal antibody (ATZ11) that specifically recognizes a conformation-dependent neoepitope on polymerized alpha(1)-antitrypsin to detect polymers within hepatocytes of individuals with alpha(1)-antitrypsin deficiency. Paraffin-embedded liver tissue specimens were obtained from individuals who were homozygous for the Z (Glu342Lys), Mmalton (52Phe del), and Siiyama (Ser53Phe) alleles of alpha(1)-antitrypsin that result in hepatic inclusions and profound plasma deficiency. Immunohistological staining with a polyclonal anti-human alpha(1)-antitrypsin antibody showed hepatic inclusions in all 3 cases, while ATZ11 reacted with hepatic inclusions formed by only Z alpha(1)-antitrypsin. Polymers of plasma M and Z alpha(1)-antitrypsin prepared under different conditions in vitro and polymers of recombinant mutants of alpha(1)-antitrypsin demonstrated that the monoclonal antibody detected a neoepitope on the polymerized protein. It did not detect polymers formed by a recombinant shutter domain mutant (that mirrors the effects of the Siiyama and Mmalton variants), polymers formed by cleaving alpha(1)-antitrypsin at the reactive loop, or C-sheet polymers formed by heating alpha(1)-antitrypsin in citrate. In conclusion, the ATZ11 monoclonal antibody detects Z alpha(1)-antitrypsin in hepatic inclusions by detecting a neoepitope that is specific to the polymeric conformer and that is localized close to residue 342.

Protease inhibitor phenotypes and serum alpha-1-antitrypsin levels in patients with COPD: A study from Hong Kong

OBJECTIVE

Many studies have suggested that an imbalance of protease activation and inhibition might result in COPD with emphysema. Levels of alpha-1-antitrypsin (alpha1-AT), the key protease inhibitor, are genetically determined by alleles that present in many phenotypes/subtypes, some of which are associated with deficiency of the protein. We prospectively evaluated the prevalence of the protease inhibitor (Pi) alleles and phenotypes together with the serum alpha1-AT levels in Chinese patients with COPD.

METHODOLOGY

The study population comprised 356 patients with COPD. The male-to-female ratio was 4 : 1 with a mean age of 72.4 years (range 44-93 years). Isoelectric focusing was used for Pi phenotyping/subtyping. The frequencies of Pi alleles and phenotypes were compared with the frequencies in 1085 healthy unrelated Chinese control subjects. The serum alpha1-AT levels were measured by the Cobas Fara assay.

RESULTS

PiZ was not detected. No significant difference in distribution of PiM phenotypes/subtypes between patients with COPD and healthy controls was observed, except for M1M3 and M2M3. There was also a significant difference in the proportion of variant S and F alleles between the disease group and the control population.

CONCLUSION

The low prevalence of deficiency Pi phenotypes/subtypes suggests a lack of contribution of alpha1-AT deficiency to the pathogenesis of COPD in Chinese patients. The strategy of launching an alpha1-AT deficiency detection program among COPD patients, based on the recommendation of the World Health Organization, may not be readily applicable in our local setting.

What We Owe to α1‐Antitrypsin and to Carl‐Bertil Laurell

The archetypal status of alpha(1)-antitrypsin in biology and medicine grew from the finding, thirty years ago, by Carl-Bertil Laurell, of the association of its deficiency with emphysema. In biology, alpha(1)-antitrypsin now provides the model for both the structure and the remarkable mechanism of the serpin protease inhibitors that control the key proteolytic pathways of the body. In medicine, the plasma deficiency of alpha(1)-antitrypsin has drawn attention to protease-antiprotease imbalance as a contributory cause of chronic obstructive pulmonary disease. But even more significantly, the finding that the common genetic deficiency of alpha(1)-antitrypsin was also associated with the development of liver cirrhosis introduced the new entity of the conformational diseases. The proposal that the same general mechanism was responsible for the best known of the conformational diseases, the common late-onset dementias, was controversial. It was vindicated however by the recent finding that a mutation, which results in the liver aggregation of alpha(1)-antitrypsin, also results in a typical late-onset dementia when it occurs in a brain-specific homologue of alpha(1)-antitrypsin. The extensive development of such diverse fields of studies, each based on alpha(1)-antitrypsin, is a measure of the encouragement Laurell gave to younger colleagues in the field. It also reflects the great advantage of linked contributions from clinical as well as basic sciences. Time after time, scientific controversies and deadlocks have been solved by landmark clinical cases, which have revealed unexpected findings and insights, within and beyond the fields of study.

MVarallo: A New MLike Alpha 1-Antitrypsin-Deficient Allele

A 73-year-old never-smoker woman with chronic bronchitis, increasing dyspnoea, and airflow limitation with a FEV1 of 49% of predicted value had low serum level of alpha-1-antitrypsin (69 mg/dL, normal range 150-350). Isoelectric focusing showed an Mlike pattern. Direct sequencing showed, in the second exon, a particular DNA alteration localized between codon 41 and codon 51: a region of 30 base pairs (bp) was completely deleted and substituted by a 22-bp sequence. The resulting loss of 8 bp yields, in the second exon, a 70-71 stop codon. This new Mlike variant was denominated MVarallo from the site where it was discovered.

Conserved Ser residues, the shutter region, and speciation in serpin evolution

The suicide inhibitory mechanism of serine protease inhibitors of the serpin superfamily depends heavily on their structural flexibility, which is controlled in large part by the breach and shutter regions of the central Abeta-sheet. We examined codon usage by the highly conserved residues, Ser-53 and Ser-56, of the shutter region and found a TCN-AGY usage dichotomy for Ser-56 that remarkably is linked to the protostome-deuterostome split. Our results suggest that serpin evolution was driven by phylogenetic speciation and not pressure to fulfill new physiologic functions mitigating against coevolution with the family of serine proteases they inhibit.

A novel mode of polymerization of alpha1-proteinase inhibitor

Patients homozygous for the Z mutant form of alpha1-proteinase inhibitor (alpha1-PI) have an increased risk for the development of liver disease because of the accumulation in hepatocytes of inclusion bodies containing linear polymers of mutant alpha1-PI. The most widely accepted model of polymerization proposes that a linear, head-to-tail polymer forms by sequential insertion of the reactive center loop (RCL) of one alpha1-PI monomer between the central strands of the A beta-sheet of an adjacent monomer. This model derives primarily from two observations: peptides that are homologous with the RCL insert into the A beta-sheet of alpha1-PI monomer and this insertion prevents alpha1-PI polymerization. Normal alpha1-PI monomer does not spontaneously polymerize; however, here we show that the disulfide-linked dimer of normal alpha1-PI spontaneously forms linear polymers in buffer. The monomers within this dimer are joined head-to-head. Thus, the arrangement of monomers in these polymers must be different from that predicted by the loop-A sheet model. Therefore, we propose a new model for alpha1-PI polymer. In addition, polymerization of disulfide-linked dimer is not inhibited by the presence of the peptide even though dimer appears to interact with the peptide. Thus, RCL insertion into A beta-sheets may not occur during polymerization of this dimer.

Serpin polymerization is prevented by a hydrogen bond network that is centered on his-334 and stabilized by glycerol

Polymerization of serpins commonly results from mutations in the shutter region underlying the bifurcation of strands 3 and 5 of the A-sheet, with entry beyond this point being barred by a H-bond network centered on His-334. Exposure of this histidine in antithrombin, which has a partially opened sheet, allows polymerization and peptide insertion to occur at pH 6 or less when His-334 will be predictably protonated with disruption of the H-bond network. Similarly, thermal stability of antithrombin is pH-dependent with a single unfolding transition at pH 6, but there is no such transition when His-334 is buried by a fully closed A-sheet in heparin-complexed antithrombin or in alpha(1)-antitrypsin. Replacement of His-334 in alpha(1)-antitrypsin by a serine or alanine at pH 7.4 results in the same polymerization and loop-peptide acceptance observed with antithrombin at low pH. The critical role of His-334 and the re-formation of its H-bond network by the conserved P8 threonine, on the full insertion of strand 4, are relevant for the design of therapeutic blocking agents. This is highlighted here by the crystallographic demonstration that glycerol, which at high concentrations blocks polymerization, can replace the P8 threonine and re-form the disrupted H-bond network with His-334.

Serpinopathies and the conformational dementias

The serpin superfamily of serine proteinase inhibitors has a central role in controlling proteinases in many biological pathways in a wide range of species. The inhibitory function of the serpins involves a marked conformational transition, but this inherent molecular flexibility also renders the serpins susceptible to point mutations that result in aberrant intermolecular linkage and polymer formation. The effects of such protein aggregation are cumulative, with a progressive loss of cellular function that results in diseases as diverse as cirrhosis and emphysema. The recent recognition that mutations in a serpin can also result in late-onset dementia provides insights into changes that underlie other conformational diseases, such as the amyloidoses, the prion encephalopathies and Huntington and Alzheimer diseases.

Familial conformational diseases and dementias

Familial conformational diseases occur when a mutation alters the conformation of a protein resulting in abnormal intermolecular interactions, protein aggregation, and consequent tissue damage. The molecular mechanisms of conformational disease are best understood for the serine protease inhibitor (serpin) superfamily of proteins. The serpinopathies include alpha(1)-antitrypsin (SERPINA1) deficiency and the newly characterized familial encephalopathy with neuroserpin inclusion bodies (FENIB) resulting from mutations in the neuroserpin (SERPINI1) gene. This review discusses how insights gained from the study of the serpins may be used to guide our research into other common diseases such as Alzheimer disease, Huntington disease, and Parkinson disease.

The molecular basis for anti-proteolytic and non-proteolytic functions of plasminogen activator inhibitor type-1: roles of the reactive centre loop, the shutter region, the flexible joint region and the small serpin fragment

The serine proteinase inhibitor plasminogen activator inhibitor type-1 (PAI-1) is the primary physiological inhibitor of the tissue-type and the urokinase-type plasminogen activator (tPA and uPA, respectively) and as such an important regulator of proteolytic events taking place in the circulation and in the extracellular matrix. Moreover, a few non-proteolytic functions have been ascribed to PAI-1, mediated by its interaction with vitronectin or the interaction between the uPA-PAI-1 complex bound to the uPA receptor and members of the low density lipoprotein receptor family. PAI-1 belongs to the serpin family, characterised by an unusual conformational flexibility, which governs its molecular interactions. In this review we describe the anti-proteolytic and non-proteolytic functions of PAI-1 from both a biological and a biochemical point of view. We will relate the various biological roles of PAI-1 to its biochemistry in general and to the different conformations of PAI-1 in particular. We put emphasis on the intramolecular rearrangements of PAI-1 that are required for its antiproteolytic as well as its non-proteolytic functions.

Molecular characterization of four alpha-1-antitrypsin variant alleles found in a Japanese population: a mutation hot spot at the codon for amino acid 362

In this study alpha-1-antitrypsin (AAT) phenotypes at the protease inhibitor (PI) locus were determined by isoelectric focusing of native and desialylated serum samples from 236 Japanese subjects living in the western part of Japan. The shifts in relative mobility between some PI types were observed before and after desialylation. This technique was useful in distinguishing between some PI M subtypes and variants. The molecular basis of four variant alleles, including two new alleles found in this study, was characterized: PI E(tokyo) [Lys(335)(AAG)--> Glu(GAG)] and PI N(nagato) [Leu(276)(CTG)-->Pro(CCG)] arose from PI M1(Val(213)) and PI M2, respectively. A new PI P(yonago) [Asp(19)(GAT)-->Ala(GCT)] originated from PI M1(Val(213)). A new PI M5(gunma) [Pro(362)(CCC)-->Ser(TCC)], arising from PI M3, was the sixth allele involving a mutation at codon 362, which is suggested to be a mutation hot spot. PI M5(gunma) was likely to show normal AAT levels and function although the mutations occurred near codon 358 for Met(358). The molecular basis of PI variant alleles found in Japanese was different from that reported in previous studies.

Importance of the amino-acid composition of the shutter region of plasminogen activator inhibitor-1 for its transitions to latent and substrate forms

The serpins are of general protein chemical interest due to their ability to undergo a large conformational change consisting of the insertion of the reactive centre loop (RCL), which becomes strand 4, into the central beta sheet A. To make space for the incoming RCL, the 'shutter region' opens by the beta strands 3A and 5A sliding apart over the underlying alpha helix B. Loop insertion occurs during the formation of complexes of serpins with their target serine proteinases and during latency transition. This type of loop insertion is unique to plasminogen activator inhibitor-1 (PAI-1). We report here that amino-acid substitutions in a buried cluster of three residues forming a hydrogen bonding network in the shutter region drastically accelerate PAI-1 latency transition; that the rate was in all cases normalized by the PAI-1 binding protein vitronectin; and that substitution of an adjacent beta strand 5A Lys residue, believed to anchor beta strand 5A to other secondary structural elements, had differential effects on the rates of latency transition in the absence and the presence of vitronectin, respectively. An overlapping, but not identical set of substitutions resulted in an increased tendency to substrate behaviour of PAI-1 at reaction with its target proteinases. These findings show that vitronectin regulates the movements of the RCL through conformational changes of the shutter region and beta strand 5A, are in agreement with RCL insertion proceeding by different routes during latency transition and complex formation, and contribute to the biochemical basis for the potential use of PAI-1 as a therapeutic target in cancer and cardiovascular diseases.

Biochemical characterization of a neuroserpin variant associated with hereditary dementia

Neuroserpin isolated from inclusion bodies in the brain of a patient with a neurodegenerative disease was characterized biochemically. The protein consisted of residues 20 to 410 of the neuroserpin precursor deduced from its cDNA sequence indicating the entire molecule was deposited. A minor amount started with residue 19 of the precursor, and the carboxyl terminus was heterogeneous ending at residues 405, 407, 409, and 410. Arg was present at position 52. No normal Ser52 was found indicating that only mutant neuroserpin was present in the inclusion bodies. The three potential Asn glycosylation sites all contained carbohydrate. DNA sequence analysis of exons 2 to 9 of the neuroserpin gene in the proband showed the published normal neuroserpin sequence except for the presence of both adenine and cytosine at the first position of codon 52, that indicates heterozygosity for both the normal Ser(AGT) and variant Arg(CGT) at this position in the expressed protein. Restriction fragment length polymorphism analysis of a polymerase chain reaction product from exon 2 revealed the propositus and his affected sibling both were heterozygous for the mutation whereas 100 unaffected controls were negative. Chemical characterization of the variant neuroserpin will significantly enhance the understanding of this protein in both normal physiology and neurodegenerative diseases.

Conformational changes in serpins: I. The native and cleaved conformations of alpha(1)-antitrypsin

The serpins (SERine Proteinase INhibitors) are a family of proteins with important physiological roles, including but not limited to the inhibition of chymotrypsin-like serine proteinases. The inhibitory mechan- ism involves a large conformational change known as the S-->R (stressed-->relaxed) transition. The largest structural differences occur in a region around the scissile bond called the reactive centre loop: In the native (S) state, the reactive centre is exposed, and is free to interact with proteinases. In inhibitory serpins, in the cleaved (R) state the reactive centre loop forms an additional strand within the beta-sheet. The latent state is an uncleaved state in which the intact reactive centre loop is integrated into the A sheet as in the cleaved form, to give an alternative R state. The serpin structures illustrate detailed control of conformation within a single protein. Serpins are also an unusual family of proteins in which homologues have native states with different folding topologies. Determination of the structures of inhibitory serpins in multiple conformational states permits a detailed analysis of the mechanism of the S-->R transition, and of the way in which a single sequence can form two stabilised states of different topology. Here we compare the conformations of alpha(1)-antitrypsin in native and cleaved states. Many protein conformational changes involve relative motions of large rigid subunits. We determine the rigid subunits of alpha(1)-antitrypsin and analyse the changes in their relative position and orientation. Knowing that the conformational change is initiated by cleavage at the reactive centre, we describe a mechanism of the S-->R transition as a logical sequence of mechanical effects, even though the transition likely proceeds in a concerted manner.

Familial dementia caused by polymerization of mutant neuroserpin

Aberrant protein processing with tissue deposition is associated with many common neurodegenerative disorders; however, the complex interplay of genetic and environmental factors has made it difficult to decipher the sequence of events linking protein aggregation with clinical disease. Substantial progress has been made toward understanding the pathophysiology of prototypical conformational diseases and protein polymerization in the superfamily of serine proteinase inhibitors (serpins). Here we describe a new disease, familial encephalopathy with neuroserpin inclusion bodies, characterized clinically as an autosomal dominantly inherited dementia, histologically by unique neuronal inclusion bodies and biochemically by polymers of the neuron-specific serpin, neuroserpin. We report the cosegregation of point mutations in the neuroserpin gene (PI12) with the disease in two families. The significance of one mutation, S49P, is evident from its homology to a previously described serpin mutations, whereas that of the other, S52R, is predicted by modelling of the serpin template. Our findings provide a molecular mechanism for a familial dementia and imply that inhibitors of protein polymerization may be effective therapies for this disorder and perhaps for other more common neurodegenerative diseases.

Heteropolymerization of S, I, and Z alpha1-antitrypsin and liver cirrhosis

The association between Z alpha1-antitrypsin deficiency and juvenile cirrhosis is well-recognized, and there is now convincing evidence that the hepatic inclusions are the result of entangled polymers of mutant Z alpha1-antitrypsin. Four percent of the northern European Caucasian population are heterozygotes for the Z variant, but even more common is S alpha1-antitrypsin, which is found in up to 28% of southern Europeans. The S variant is known to have an increased susceptibility to polymerization, although this is marginal compared with the more conformationally unstable Z variant. There has been speculation that the two may interact to produce cirrhosis, but this has never been demonstrated experimentally. This hypothesis was raised again by the observation reported here of a mixed heterozygote for Z alpha1-antitrypsin and another conformationally unstable variant (I alpha1-antitrypsin; 39Arg-->Cys) identified in a 34-year-old man with cirrhosis related to alpha1-antitrypsin deficiency. The conformational stability of the I variant has been characterized, and we have used fluorescence resonance energy transfer to demonstrate the formation of heteropolymers between S and Z alpha1-antitrypsin. Taken together, these results indicate that not only may mixed variants form heteropolymers, but that this can causally lead to the development of cirrhosis.

Alpha 1-antitrypsin deficiency. A conformational disease

The serpin family of protease inhibitors, to which alpha 1-antitrypsin belongs, has the unique feature of a mobile reactive center. Mutations within the critical regions of the molecule that control this mobility can allow premature changes in conformation with consequent abnormalities in folding and accompanying polymer formation. These abnormalities explain the plasma deficiency and liver inclusions associated with the common Z variant, as well as other variants of alpha 1-antitrypsin. The understanding of the molecular mechanisms provides a satisfying explanation for the clinical findings associated with these deficiency variants.

Alpha-1-antitrypsin deficiency: biochemistry and clinical manifestations

Alpha-1-antitrypsin (alpha 1-AT) deficiency is a well known cause of emphysema in adults. A subgroup of deficient individuals develops liver injury during infancy and childhood. In fact, it is the most common genetic cause of liver disease in children. Although lung injury is due to the decrease in alpha 1-AT function in the lung, allowing uninhibited elastolytic destruction of its connective tissue integrity, liver injury is probably due to retention of the mutant alpha 1-AT molecule in the endoplasmic reticulum (ER) of liver cells. Recent studies have shown that the mutant alpha 1-AT molecule polymerizes in the ER by a novel loop-sheet insertion mechanism. Other recent studies show that the subgroup of deficient individuals is susceptible to liver injury by virtue of unlinked genetic traits and/or environmental factors which interfere with degradation of the mutant alpha 1-AT molecules within the ER.

The structural puzzle of how serpin serine proteinase inhibitors work

Serine proteinase cleavage of proteins is essential to a wide variety of biological processes and is primarily regulated by protein inhibitors. Many inhibitors are conformationally rigid simulations of optimal serine proteinase substrates, which makes them highly efficient competitive inhibitors of target proteinases. In contrast, members of the serpin family of serine proteinase inhibitors display extensive flexibility and polymorphism, particularly in their reactive site segments and in beta-sheet secondary structure, which can take up and expel strands. Reactive site and beta-sheet polymorphism appear to be coupled in the serpins and may account for the extreme stability of serpin-proteinase complexes through the insertion of the reactive site strand into a beta-sheet. These unusual properties may have opened an adaptive pathway of proteinase regulation that was unavailable to the conformationally rigid proteinase inhibitors.

Genomic structure and PCR-SSCP analysis of the human CD40 ligand gene: its application to prenatal screening for X-linked hyper-IgM syndrome

To develop a general method for analysis of the mutation and prenatal diagnosis of X-linked hyper-IgM syndrome (XHM), the human CD40 ligand (hCD40L) gene was cloned and sequenced with special reference to the 5' and 3' flanking regions and exon/intron boundaries. The hCD40L gene consists of five exons and four introns, as already reported by others. Two major transcription initiation sites were identified at 67 bp and 64 bp upstream from the ATG initiation codon. The hCD40L mRNA transcripts terminated at 321 bp, 327 bp and 987 bp downstream from the TGA stop codon. Based on the intronic sequences, oligonucleotide primers were designed for amplifying the coding region of each exon separately. Polymerase chain reaction--single-strand conformational polymorphism (PCR-SSCP) analysis was successfully applied to screening for the defective hCD40L gene in a family with XHM. The nonsense mutation, Trp140 (TGG)-->stop (TAG) in exon 5, was found in the mother and an affected child. We also performed prenatal diagnosis by PCR-SSCP during the first trimester of pregnancy in this family.

alpha 1-Antitrypsin Mmalton (Phe52-deleted) forms loop-sheet polymers in vivo. Evidence for the C sheet mechanism of polymerization

The Z (Glu342-->Lys) and Siiyama (Ser53-->Phe) deficiency variants of alpha 1-antitrypsin result in the retention of protein in the endoplasmic reticulum of the hepatocyte by loop-sheet polymerization in which the reactive center loop of one molecule is inserted into a beta-pleated sheet of a second. We show here that antitrypsin Mmalton (Phe52-deleted), which is associated with the same liver inclusions, is also retained at an endoglycosidase H-sensitive stage of processing in the Xenopus oocyte and spontaneously forms polymers in vivo. These polymers, obtained from the plasma of an Mmalton/QO (null) bolton heterozygote, were much shorter than other antitrypsin polymers and contained a reactive center loop-cleaved species. Monomeric mutant antitrypsin was also isolated from the plasma. The monomeric component had a normal unfolding transition on transverse urea gradient gel electrophoresis and formed polymers in vitro more readily than M, but less readily than Z, antitrypsin. The A beta-sheet accommodated a reactive center loop peptide much less readily than Z antitrypsin, which in turn was less receptive than native M antitrypsin. The nonreceptive conformation of the A sheet in antitrypsin Mmalton had little effect on kinetic parameters, the formation of SDS-stable complexes, the S to R transition, and the formation of the latent conformation. Comparison of the results with similar findings of short chain polymers associated with the antithrombin variant Rouen VI (Bruce, D., Perry, D., Borg, J.-Y., Carrell, R. W., and Wardell, M. R. (1994) J. Clin. Invest. 94, 2265-2274) suggests that polymerization is more complicated than the mechanism proposed earlier. The Z, Siiyama, and Mmalton mutations favor a conformational change in the antitrypsin molecule to an intermediate between the native and latent forms. This would involve a partial overinsertion of the reactive loop into the A sheet with displacement of strand 1C and consequent loop-C sheet polymerization.