Tau protein hyperphosphorylation in sporadic ALS with cognitive impairment

The authors have characterized frontal cortical tau protein in cognitively intact (4) and cognitively impaired (ALSci, 4) ALS patients and compared it with control (2) or Alzheimer disease (AD, 1)- derived tau. The authors observed expression of both 3R and 4R tau isoforms; increased insoluble tau protein; phosphatase resistance; and hyperphosphorylation at T175, S208, and S210. Soluble tau from both AD and ALSci was also phosphorylated at S237. Tau hyperphosphorylation is associated with ALS.

Allelic variants of the canine heavy neurofilament (NFH) subunit and extensive phosphorylation in dogs with motor neuron disease

Aberrant accumulation of extensively phosphorylated heavy (high molecular weight) neurofilament (NFH) and neurodegeneration are features of hereditary canine spinal muscular atrophy (HCSMA), an animal model of human motor neuron disease. In this study, the canine NFH gene was mapped, cloned, and sequenced, and electrospray/mass spectrometry was used to evaluate the phosphorylation state of NFH protein from normal dogs and dogs with HCSMA. The canine NFH gene was localized to a region on canine chromosome 26 that corresponds to human NFH on chromosome 22q. The predicted length of the canine NFH protein is 1135 amino acids, and it shares an 80.3% identity with human NFH and >74.6% with murine NFH proteins. Direct sequencing of NFH cDNA from HCSMA dogs revealed no mutations, although cDNA sequence and restriction fragment length polymorphism (RFLP) analysis indicates that there are at least three canine NFH alleles, differing in the position and number (61 or 62) of Lys-Ser-Proline (KSP) motifs. The two longest alleles (L1 and L2), each with 62 KSP repeats, contain an additional 24-base insert and were observed in both normal and HCSMA dogs. However, the shorter allele (the C allele), with 61 KSP sites and lacking the 24-base insertion, was absent in dogs with HCSMA. Mass spectrometry data indicated that almost all of the NFH KSP phosphorylation sites were occupied. No new or extra sites were identified in native NFH purified from the HCSMA dogs. The predominance of the two longest NFH alleles and the additional KSP phosphorylation sites they confer probably account for the presence of extensively phosphorylated NFs detected immunohistochemically in dogs with HCSMA.

Identification of novel phosphorylation sites on postsynaptic density proteins

Phosphorylation of the components of the postsynaptic density (PSD), a protein complex lining the postsynaptic membrane, may regulate synaptic structure and function. We carried out mass spectrometric analyses to identify phosphorylation sites on PSD proteins. Phosphopeptides were isolated from the total tryptic digest of a PSD fraction by immobilized metal affinity chromatography and analyzed by liquid chromatography and tandem mass spectrometry. The phosphorylated residues detected following in vitro phosphorylation in the presence of Ca2+/calmodulin included S-1058 on SynGAP and S-1662 and S-1668 on Shank3. Other phosphorylated residues were identified in control samples, presumably reflecting phosphorylation in the intact cell. These included the homologous residues, S-295 on PSD-95 and S-365 on PSD-93, located between the PDZ2 and PDZ3 domains of these proteins; and S-367 located on the actin-binding domain of beta-CaMKII. The sequence RXXSPV emerged as a common phosphorylation motif of three specialized PSD scaffolding proteins, PSD-95, PSD-93, and Shank3. Phosphorylated serine residues in several of the identified phosphorylation sites were followed by prolines, suggesting prominent involvement of proline directed kinases in the regulation of PSD components.

Human papillomaviruses and cancer in Uganda

In a case-control study in Uganda, we examined associations between different cancer sites or types in relation to antibodies against human papillomaviruses (HPV)-16, -18 and -45. For each cancer site or type, the control group comprised all other cancers excluding those known, or thought to be associated with HPV infection (cancers of the uterine cervix, penis and eye). Among controls the seroprevalence of antibodies was 11% (68/616) against HPV-16, 5% (29/605) against HPV-18 and 6% (35/605) against HPV-45. Antibodies against HPV-16 were significantly associated with only two cancers: uterine cervix [prevalence of antibodies 27% (51/191); odds ratio (OR) 2.0, 95% confidence interval (CI) 1.2-3.1, P=0.01] and penis [prevalence of antibodies 27% (4/15); OR 6.4, 95% CI 1.7-24.3, P=0.01]. For both cancers, the risk increased with increasing anti-HPV-16 antibody titre (Ptrend=0.01 for each). No cancer site or type was significantly associated with antibodies against HPV-18 and -45.

Infection with Kaposi's sarcoma-associated herpesvirus (KSHV) and human immunodeficiency virus (HIV) in relation to the risk and clinical presentation of Kaposi's sarcoma in Uganda

A case-control study from Uganda found that the risk of Kaposi's sarcoma increased with increasing titre of antibodies against Kaposi's sarcoma-associated herpesvirus (KSHV) latent nuclear antigens, independently of HIV infection. Clinically, widespread Kaposi's sarcoma was more frequent among patients with HIV infection than in those without, but was not related to anti-KSHV antibody titres.

The epidemiology of conjunctival squamous cell carcinoma in Uganda

As part of a larger investigation of cancer in Uganda, we conducted a case-control study of conjunctival squamous cell carcinoma in adults presenting at hospitals in Kampala. Participants were interviewed about social and lifestyle factors and had blood tested for antibodies to HIV, KSHV and HPV-16, -18 and -45. The odds of each factor among 60 people with conjunctival cancer was compared to that among 1214 controls with other cancer sites or types, using odds ratios, estimated with unconditional logistic regression. Conjunctival cancer was associated with HIV infection (OR 10.1, 95% confidence intervals [CI] 5.2-19.4; P<0.001), and was less common in those with a higher personal income (OR=0.4, 95% CI 0.3-0.7; P<0.001)[corrected]. The risk of conjunctival cancer increased with increasing time spent in cultivation and therefore in direct sunlight (chi2 trend=3.9, P=0.05), but decreased with decreasing age at leaving home (chi2 trend=3.9, P=0.05), perhaps reflecting less exposure to sunlight consequent to working in towns, although both results were of borderline statistical significance. To reduce confounding, sexual and reproductive variables were examined among HIV seropositive individuals only. Cases were more likely than controls to report that they had given or received gifts for sex (OR 3.5, 95% CI 1.2-10.4; P=0.03), but this may have been a chance finding as no other sexual or reproductive variable was associated with conjunctival cancer, including the number of self-reported lifetime sexual partners (P=0.4). The seroprevalence of antibodies against HPV-18 and -45 was too low to make reliable conclusions. The presence of anti-HPV-16 antibodies was not significantly associated with squamous cell carcinoma of the conjunctiva (OR 1.5, 95% CI 0.5-4.3; P=0.5) and nor were anti-KSHV antibodies (OR 0.9, 95% CI 0.4-2.1; P=0.8). The 10-fold increased risk of conjunctival cancer in HIV infected individuals is similar to results from other studies. The role of other oncogenic viral infections is unclear.

Identification of four additional myoinhibitory peptides (MIPs) from the ventral nerve cord of Manduca sexta

Four new myoinhibitory peptides were isolated and identified from the ventral nerve cord of adult Manduca sexta. The new peptides are related to two previously identified myoinhibitory peptides also isolated from adult M. sexta, Mas-MIP I and Mas-MIP II. The sequences of the new peptides are APEKWAAFHGSWamide (Mas-MIP III), GWNDMSSAWamide (Mas-MIP IV), GWQDMSSAWamide (Mas-MIP V), and AWSALHGAWamide (Mas-MIP VI). Mas-MIPs III-VI were found to inhibit spontaneous peristalsis of the adult M. sexta anterior hindgut (ileum) in vitro.

Testis ecdysiotropin, an insect gonadotropin that induces synthesis of ecdysteroid

Testes of lepidoptera synthesized ecdysteroid in a somewhat different temporal pattern than the prothoracic glands that release ecdysteroid to the hemolymph. Brain extracts from Heliothis virescens and Lymantria dispar induced testes to synthesize ecdysteroid, but did not affect prothoracic glands. The testis ecdysiotropin (LTE) was isolated from L. dispar pupal brains by a series of high-pressure chromatography steps. Its sequence was Ile-Ser-Asp-Phe-Asp-Glu-Tyr-Glu-Pro-Leu-Asn-Asp-Ala-Asp-Asn-Asn-Glu-Val-Leu-Asp-Phe-OH, of molecular mass 2,473 Daltons. The predominant signaling pathway for LTE was via G(i) protein, IP3, diacylglycerol and PKC; a modulating pathway, apparently mediated by an angiotensin II-like peptide, was controlled via G(s) protein, cAMP, and PKA. Testis ecdysteroid caused isolated testis sheaths to also synthesize a growth factor that induced development of the male genital tract. The growth factor appeared to be a glycoprotein similar to vertebrate alpha-1-glycoprotein. A polyclonal antibody to LTE indicated LTE-like peptide in L. dispar brain medial neurosecretory cells, the suboesophageal, and other ganglia, and also in its target organ, the testis sheath. LTE immunoreactivity was also seen in testis sheaths of Rhodnius prolixus. LTE-like immunoactivity was also detected in developing optic lobes, antennae, frontal ganglia, and elongating spermatids of developing L. dispar pupae. This may indicate that LTE has a role in development as well as stimulation of testis ecdysteroid synthesis. Published 2001 Wiley-Liss, Inc.

Role of a pineal cAMP-operated arylalkylamine N-acetyltransferase/14-3-3-binding switch in melatonin synthesis

The daily rhythm in melatonin levels is controlled by cAMP through actions on the penultimate enzyme in melatonin synthesis, arylalkylamine N-acetyltransferase (AANAT; serotonin N-acetyltransferase, EC ). Results presented here describe a regulatory/binding sequence in AANAT that encodes a cAMP-operated binding switch through which cAMP-regulated protein kinase-catalyzed phosphorylation [RRHTLPAN --> RRHpTLPAN] promotes formation of a complex with 14-3-3 proteins. Formation of this AANAT/14-3-3 complex enhances melatonin production by shielding AANAT from dephosphorylation and/or proteolysis and by decreasing the K(m) for 5-hydroxytryptamine (serotonin). Similar switches could play a role in cAMP signal transduction in other biological systems.

Soluble ICAM-1 and E-selectin levels correlate with clinical and biological aspects of severe ovarian hyperstimulation syndrome

OBJECTIVE

To assess the potential involvement of the soluble endothelial cell-leukocyte adhesion molecules E-selectin and intercellular adhesion molecule-1 (ICAM-1) in the pathophysiology of capillary hyperpermeability in the ovarian hyperstimulation syndrome (OHSS).

DESIGN

Controlled clinical study.

SETTING

Women hospitalized for severe OHSS after ovulation induction for IVF at two tertiary medical centers.

PATIENT(S)

Eleven patients with severe OHSS undergoing IVF and 20 controls who had received a similar ovulation induction regimen and did not develop OHSS.

INTERVENTION(S)

Serial serum samples were obtained from all patients with OHSS from admission until discharge. Ascitic fluid was obtained from all patients by therapeutic paracentesis. Serum was obtained from all controls 4-8 days after ET.

MAIN OUTCOME MEASURE(S)

Samples were assayed for soluble E-selectin and soluble ICAM-1 by using enzyme-linked immunosorbent assay and results were correlated with clinical and biological aspects of OHSS.

RESULT(S)

Compared with controls, patients with severe OHSS had higher levels of soluble ICAM-1 and lower levels of soluble E-selectin detected in serum and ascites. Serum levels of soluble ICAM-1 decreased, while soluble E-selectin levels increased along with clinical and biological improvement. Serum soluble ICAM-1 showed significant positive correlation and serum soluble E-selectin showed significant negative correlation with clinical and biological aspects of severe OHSS.

CONCLUSION(S)

Soluble ICAM-1 and soluble E-selectin seem to be involved in the pathophysiology of capillary hyperpermeability in severe OHSS.

A case-control study of human immunodeficiency virus infection and cancer in adults and children residing in Kampala, Uganda

Uganda offers a unique setting in which to study the effect of human immunodeficiency virus-1 (HIV-1) on cancer. HIV-1 is prevalent there, and cancers which are known to be HIV-associated, such as Kaposi's sarcoma and Burkitt's lymphoma, are endemic. Adults residing in Kampala, Uganda, presenting with cancer in city hospitals were interviewed and had an HIV test. Of the 302 adults recruited, 190 had cancers with a potentially infectious aetiology (cases). The remaining 112 adults with tumours not known to have an infectious aetiology formed the control group. In addition, 318 children who were also Kampala residents were recruited and tested for HIV: 128 with cancer (cases) and 190 with non-malignant conditions (controls). HIV seroprevalence was 24% in adult controls and 6% in childhood controls. The odds of HIV seropositivity among cases with specific cancers (other than Kaposi's sarcoma in adults) were compared with that among controls, using odds ratios (ORs), estimated with unconditional logistic regression. All ORs were adjusted for age (<5, 5-14, 15-19, 30-44, 45+) and sex and, in adults, also for the number of lifetime sexual partners (1 or 2, 3-9, 10+). In adults, HIV infection was associated with a significantly (p < 0.05) increased risk of non-Hodgkin's lymphoma [OR = 6.2, 95% confidence interval (CI) 1.9-19.9, based on 21 cases] and conjunctival squamous-cell carcinoma (OR = 10.9, 95% CI 3.1-37.7, based on 22 cases) but not with cancer at other common sites, including liver and uterine cervix. In children, HIV infection was associated with a significantly increased risk of Kaposi's sarcoma (OR = 94.9, 95% CI 28.5-315.3, based on 36 cases) and Burkitt's lymphoma (OR = 7.5, 95% CI 2.8-20.1, based on 33 cases) but not with other cancers. The pattern of HIV-associated cancers in Uganda is broadly similar to that described elsewhere, but the relative frequency of specific cancers, such as conjunctival carcinoma, in HIV-infected people differs.

Phosphorylation state of the native high-molecular-weight neurofilament subunit protein from cervical spinal cord in sporadic amyotrophic lateral sclerosis

The intraneuronal aggregation of phosphorylated high-molecular-weight neurofilament protein (NFH) in spinal cord motor neurons is considered to be a key pathological marker of amyotrophic lateral sclerosis (ALS). In order to determine whether this observation is due to the aberrant or hyper-phosphorylation of NFH, we have purified and characterized NFH from the cervical spinal cords of ALS patients and controls. We observed no differences between ALS and normal controls in the physicochemical properties of NFH in Triton X-100 insoluble protein fractions, with respect to migration patterns on 2D-iso electrofocusing (IEF) gels, the rate of Escherichia coli alkaline phosphatase mediated dephosphorylation, or the rate of calpain-mediated proteolysis. The rate of calpain-mediated proteolysis was unaffected by either exhaustive NFH dephosphorylation or by the addition of calmodulin to the reaction. Phosphopeptides and the phosphorylated motifs characterized by liquid chromatography tandem mass spectroscopy (LC/MS/MS) analysis demonstrated that all the phosphorylated residues found in ALS NFH were also found to be phosphorylated in normal human NFH samples. Hence, we have observed no difference in the physicochemical properties of normal and ALS NFH extracted from cervical spinal cords, suggesting that the perikaryal aggregation of highly phosphorylated NF in ALS neurons reflects the aberrant somatotopic localization of normally phosphorylated NFH.

Characterization of the phosphorylation sites of the squid (Loligo pealei) high-molecular-weight neurofilament protein from giant axon axoplasm

Axonal caliber in vertebrates is attributed, in part, to the extensive phosphorylation of NFM and NFH C-terminal tail domain KSP repeats by proline-directed kinases. The squid giant axon, primarily involved in rapid impulse conduction during jet propulsion motility, is enriched in squid-specific neurofilaments, particularly the highly phosphorylated NF-220. Of the 228 serine-threonine candidate phosphate acceptor sites in the NF-220 tail domain (residues 401-1220), 82 are found in numerous repeats of three different motifs SAR/K, SEK/R, K/RSP, with 62 of these tightly clustered in the C-terminal repeat segment (residues 840-1160). Characterization of the in vivo NF-220 phosphorylated sites should provide clues as to the relevant kinases. To characterize these sites, proteolytic digests of NF-220 were analyzed by a combination of HPLC, electrospray tandem mass spectrometry and database searching. A total of 53 phosphorylation sites were characterized, with 47 clustered in the C-terminal repeat segment (residues 840-1160), representing 76% (47/62) of the total acceptor sites in the region. As in mammalian NFH, approximately 64% of the K/RSP sites (14/22) in this region were found to be phosphorylated implicating proline-directed kinases. Significantly, 78% of serines (31/40) in the KAES*EK and EKS*ARSP motifs were also phosphorylated suggesting that non proline-directed kinases such as CKI may also be involved. This is consistent with previous studies showing that CKI is the principal kinase associated with axoplasmic NF preparations. It also suggests that phosphorylation of large macromolecules with multiple phospho-sites requires sequential phosphorylation by several kinases.

Efficacy of postexposure prophylaxis after intravaginal exposure of pig-tailed macaques to a human-derived retrovirus (human immunodeficiency virus type 2)

Postexposure prophylaxis (PEP) after intravaginal exposure to human immunodeficiency virus (HIV) was investigated using the HIV type 2 (HIV-2)/pig-tailed macaque transmission model. PEP for 28 days with the reverse transcriptase inhibitor (R)-9-(2-phosphonylmethoxypropyl)adenine (PMPA; tenofovir) was initiated 12 to 72 h following HIV-2 exposure. Systemic infection was not evident in the 12- and 36-h groups, as defined by plasma viremia, cell-associated provirus, antibody responses, and lymph node virus. Breakthrough infection in the 72-h group was detected at week 16 post-virus exposure. These results demonstrate for the first time using a vaginal transmission model that early intervention after high-risk sexual exposures may prevent infection.

Evidence for expression of some microtubule-associated protein 1B in neurons as a plasma membrane glycoprotein

Microtubule-associated protein (MAP) 1B is a high-molecular-weight cytoskeletal protein that is abundant in developing neuronal processes and appears to be necessary for axonal growth. Various biochemical and immunocytochemical results are reported, indicating that a significant fraction of MAP1B is expressed as an integral membrane glycoprotein in vesicles and the plasma membrane of neurons. MAP1B is present in microsomal fractions isolated from developing rat brain and fractionates across a sucrose gradient in a manner similar to synaptophysin, a well-known vesicular and plasma membrane protein. MAP1B is also in axolemma-enriched fractions (AEFs) isolated from myelinated axons of rat brain. MAP1B in AEFs and membrane fractions from cultured dorsal root ganglion neurons (DRGNs) remains membrane-associated following high-salt washes and contains sialic acid. Furthermore, MAP1B in intact DRGNs is readily degraded by extracellular trypsin and is labeled by the cell surface probe sulfosuccinimidobiotin. Immunocytochemical examination of DRGNs shows that MAP1B is concentrated in vesicle-rich varicosities along the length of axons. Myelinated peripheral nerves immunostained for MAP1B show an enrichment at the axonal plasma membrane. These observations demonstrate that some of the MAP1B in developing neurons is an integral plasma membrane glycoprotein.

Evidence of avian leukosis virus subgroup E and endogenous avian virus in measles and mumps vaccines derived from chicken cells: investigation of transmission to vaccine recipients

Reverse transcriptase (RT) activity has been detected recently in all chicken cell-derived measles and mumps vaccines. A study of a vaccine manufactured in Europe indicated that the RT is associated with particles containing endogenous avian retrovirus (EAV-0) RNA and originates from the chicken embryonic fibroblasts (CEF) used as a substrate for propagation of the vaccine. We investigated the origin of RT in measles and mumps vaccines from a U.S. manufacturer and confirm the presence of RT and EAV RNA. Additionally, we provide new evidence for the presence of avian leukosis virus (ALV) in both CEF supernatants and vaccines. ALV pol sequences were first identified in particle-associated RNA by amplification with degenerate retroviral pol primers. ALV RNA sequences from both the gag and env regions were also detected. Analysis of hypervariable region 2 of env revealed a subgroup E sequence, an endogenous-type ALV. Both CEF- and vaccine-derived RT activity could be blocked by antibodies to ALV RT. Release of ALV-like virus particles from uninoculated CEF was also documented by electron microscopy. Nonetheless, infectivity studies on susceptible 15B1 chicken cells gave no evidence of infectious ALV, which is consistent with the phenotypes of the ev loci identified in the CEF. PCR analysis of ALV and EAV proviral sequences in peripheral blood mononuclear cells from 33 children after measles and mumps vaccination yielded negative results. Our data indicate that the sources of RT activity in all RT-positive measles and mumps vaccines may not be similar and depend on the particular endogenous retroviral loci present in the chicken cell substrate used. The present data do not support transmission of either ALV or EAV to recipients of the U.S.-made vaccine and provide reassurance for current immunization policies.

Prominent 85-kDa oligomannosidic glycoproteins of rat brain are signal regulatory proteins and include the SHP substrate-1 for tyrosine phosphatases

The glycoprotein component in rat brain reacting most strongly with Galanthus nivalis agglutinin (GNA) on western blots migrates as an 85-kDa band. GNA identifies mannose-rich oligosaccharides because it is highly specific for terminal alpha-mannose residues. After purification of this 85-kDa glycoprotein band by chromatography on GNA-agarose and preparative gel electrophoresis, binding of other lectins demonstrated the presence of fucose and a trace of galactose, but no sialic acid. Treatment with N-Glycanase or endoglycosidase H produced a 65-kDa band, indicating that it consisted of about one-fourth N-linked oligomannosidic carbohydrate moieties. High-performance anion-exchange chromatography and fluorescence-assisted carbohydrate electrophoresis indicated that the major carbohydrate moiety is a heptasaccharide with the structure Manalpha1-6(Manalpha1-3)Manalpha1-6(Manalpha1-3) Manbeta1-4Glc-NAcbeta1-4GlcNAc (Man5GlcNAc2). Determination of amino acid sequences of peptides produced by endoproteinase digestion demonstrated that this 85-kDa mannose-rich glycoprotein component contained the SHP substrate-1 for phosphotyrosine phosphatases and at least one other member of the signal-regulatory protein (SIRP) family. The unusually high content of oligomannosidic carbohydrate moieties on these receptor-like members of the immunoglobulin superfamily in neural tissue could be of functional significance for intercellular adhesion or signaling.

Serine-23 is a major protein kinase A phosphorylation site on the amino-terminal head domain of the middle molecular mass subunit of neurofilament proteins

We have shown previously that phosphate groups on the amino-terminal head domain region of the middle molecular mass subunit of neurofilament proteins (NF-M) are added by second messenger-dependent protein kinases. Here, we have identified Ser23 as a specific protein kinase A phosphorylation site on the native NF-M subunit and on two synthetic peptides, S1 (14RRVPTETRSSF24) and S2 (21RSSFSRVSGSPSSGFRSQSWS41), localized within the amino-terminal head domain region. Ser23 was identified as a phosphorylation site on the 32P-labeled alpha-chymotryptic peptide that carried >80% of the 32P-phosphates incorporated into the NF-M subunit by protein kinase A. The synthetic peptides S1 and S2 were phosphorylated 18 and two times more efficiently by protein kinase A than protein kinase C, respectively. Neither of the peptides was phosphorylated by casein kinase II. The sequence analyses of the chemically modified phosphorylated serine residues showed that Ser23 was the major site of phosphorylation for protein kinase A on both S1 and S2 peptides. Low levels of incorporation of 32P-phosphates into Ser22, Ser28, and Ser32 by protein kinase A were also observed. Protein kinase C incorporated 32P-phosphates into Ser22, Ser23, Ser25, Ser28, Ser32, and a threonine residue, but none of these sites could be assigned as a major site of phosphorylation. Analyses of the phosphorylated synthetic peptides by liquid chromatography-tandem mass spectrometry also showed that protein kinase A phosphorylated only one site on peptide S1 and that ions with up to four phosphates were detected on peptide S2. Analysis of the data from the tandem ion trap mass spectrometry by using the computer program PEPSEARCH did not unequivocally identify the specific sites of phosphorylation on these serine-rich peptides. Our data suggest that Ser23 is a major protein kinase A-specific phosphorylation site on the amino-terminal head region of the NF-M subunit. Phosphorylation of Ser23 on the NF-M subunit by protein kinase A may play a regulatory role in neurofilament assembly and/or the organization of neurofilaments in the axon.

Two polypeptide factors that promote differentiation of insect midgut stem cells in vitro

Isolated stem cells from the midguts of Manduca sexta and Heliothis virescens can be induced to differentiate in vitro by either of two polypeptide factors. One of the peptides was isolated from culture medium conditioned by differentiating mixed midgut cells; we used high performance liquid chromatographic separation and Edman degradation of the most prominent active peak. It is a polypeptide with 30 amino acid residues (3,244 Da), with the sequence HVGKTPIVGQPSIPGGPVRLCPGRIRYFKI, and is identical to the C-terminal peptide of bovine fetuin. A portion of this molecule (HVGKTPIVGQPSIPGGPVRLCPGRIR) was synthesized and was found to be very active in inducing differentiation of H. virescens midgut stem cells. It was designated Midgut Differentiation Factor 1 (MDF1). Proteolysis of bovine fetuin with chymotrypsin allowed isolation of a pentamer, Midgut Differentiation Factor 2 (MDF2) with the sequence HRAHY corresponding to a portion of the fetuin molecule near MDF1. Synthetic MDF2 was also biologically active in midgut stem cell bioassays. Dose response curves indicate activity in physiological ranges from 10(-14) to 10(-9) M for MDF1 and 10(-15) to 10(-5) M for MDF2.

Inhibition of T-type voltage-gated calcium channels by a new scorpion toxin

The biophysical properties of T-type voltage-gated calcium channels are well suited to pacemaking and to supporting calcium flux near the resting membrane potential in both excitable and non-excitable cells. We have identified a new scorpion toxin (kurtoxin) that binds to the alpha 1G T-type calcium channel with high affinity and inhibits the channel by modifying voltage-dependent gating. This toxin distinguishes between alpha 1G T-type calcium channels and other types of voltage-gated calcium channels, including alpha 1A, alpha 1B, alpha 1C and alpha 1E. Like the other alpha-scorpion toxins to which it is related, kurtoxin also interacts with voltage-gated sodium channels and slows their inactivation. Kurtoxin will facilitate characterization of the subunit composition of T-type calcium channels and help determine their involvement in electrical and biochemical signaling.

Characterization of serine and threonine phosphorylation sites in beta-elimination/ethanethiol addition-modified proteins by electrospray tandem mass spectrometry and database searching

A new method for the characterization of serine and threonine phosphorylation sites in proteins has been developed. After modification of a phosphoprotein by beta-elimination/ethanethiol addition and conversion of phosphoserine and phosphothreonine residues to S-ethylcysteinyl or beta-methyl-S-ethylcysteinyl residues, the modified protein was subjected to proteolytic digestion. Resulting digests were analyzed by a combination of microbore liquid chromatography, electrospray ionization tandem (MS/MS) ion trap mass spectrometry and database searching to identify original phosphorylated residues. The computer program utilized (SEQUEST) is capable of identifying peptides and modified residues from uninterpreted MS/MS spectra, and using this method, all of the five known phosphorylation sites in bovine beta-casein were identified. Application of the method to multiply phosphorylated human high molecular weight neurofilament protein (NF-H) resulted in the identification of 21 peptides and their modified residues and hence, the in vivo phosphorylation sites. These included 26 KSP and 1 KTP site, all of which occur in the KSP repeat C-terminal tail domain (residues 502-823). One site at residue 518 was previously uncharacterized. A novel non-KSP serine at residue 421 near the KLLEGEE region in a IPFSLPE motif was characterized as phosphorylated (or glycosylated). The 27 characterized phosphorylation sites occur at S/TP residues in the following motifs: KSPVKEE, KSPAEAK, KSPEKEE, KSPAEVK, KSPEKAK, KSPPEAK, KSPVKAE, and KTPAKEE. On the basis of kinase consensus sequences, all of these motifs, including the previously unreported KTPAKEE motif, can be phosphorylated by proline-directed kinases. Advantages of the new method vis-a-vis our previously reported method [Jaffe, H., Veeranna, Shetty, K. T., and Pant, H. C. (1998) Biochemistry 37, 3931-3940] include (i) production of diastereomers eluting at different retention times increased the chances of peptide identification, (ii) increased hydrophobicity and hence retention time of the modified peptides, (iii) facilitation of positive ion production, and (iv) increased susceptibility to tryptic digestion as a result of conversion of negatively charged phosphorylated residues to neutral S-ethylcysteine or beta-methyl-S-ethylcysteine residues.

Stimulation of tyrosine phosphorylation of a brain protein by hibernation

Mammalian hibernation is a state of natural tolerance to severely decreased brain blood flow. As protein tyrosine phosphorylation is believed to be involved in the development of resistance to potentially cell-damaging insults, we used immunoblotting for the phosphotyrosine moiety to analyze extracts from various tissues of hibernating and nonhibernating ground squirrels. A single, hibernation-specific phosphoprotein was detected in the brain, but not in any other tissue tested. This protein, designated pp98 to reflect its apparent molecular weight, is distributed throughout the brain, and is associated with the cellular membrane fraction. The presence of the protein is tightly linked to the hibernation state; it is not present in contemporaneously assayed animals that are exposed to the same cold temperature as the hibernators, is present for the duration of a hibernation bout (tested from 1 to 14 days), and disappears within 1 hour of arousal from hibernation. The close association of pp98 with the hibernation state, its presence in cellular membranes, and the known properties of membrane phosphotyrosine proteins suggest that it may transduce a signal for adaptation to the limited availability of oxygen and glucose and low cellular temperature that characterizes hibernation in the ground squirrel.

ω-Phonetoxin-IIA: a calcium channel blocker from the spider Phoneutria nigriventer

A peptide with neurotoxic effect on mammals, purified from the venom of the spider Phoneutria nigriventer, was studied regarding its primary structure and its effects on voltage-gated calcium channels. The peptide, named ω-phonetoxin-IIA, has 76 amino acids residues, with 14 Cys forming 7 disulphide bonds, and a molecular weight of 8362.7 Da. The neurotoxicity is a consequence of the peptide’s blocking effects on high-voltage-activated (HVA) calcium channels. N-type HVA calcium channels of rat dorsal root ganglion neurons are blocked with affinity in the sub-nanomolar concentration range. The toxin also blocks L-type channels of rat β pancreatic cells, with an affinity 40 times lower. Although not studied in detail, evidence indicates that the toxin also blocks other types of HVA calcium channels, such as P and Q. No effect was observed on low-voltage-activated, T-type calcium channels. The significant homologies between ω-phonetoxin-IIA and the peptides of the ω-agatoxin-III family, and the overlapping inhibitory effects on calcium channels are discussed in terms of the structure-activity relationship.

Characterization of myelin-associated glycoprotein (MAG) proteolysis in the human central nervous system

Purified human central nervous system myelin contains an endogenous cysteine protease which degrades the 100-kDa myelin-associated glycoprotein into a slightly smaller 90-kDa derivative called dMAG, and which has been implicated in demyelinating diseases. The native proteolytic site in human MAG was determined in order to characterize this cysteine protease in humans further. This was accomplished by identifying the carboxy-terminus of purified dMAG. The results of these experiments, in conjunction with peptidolysis assays of myelin, demonstrated that the enzyme which proteolyses MAG is extracellular and has cathepsin L-like specificity. Furthermore, it was shown that this cathepsin L-like activity potentially was regulated by the endogenous extracellular inhibitor cystatin C.

Crystallization of 5-keto-4-deoxyuronate isomerase from Escherichia coli

5-Keto-4-deoxyuronate isomerase from Escherichia coli has been crystallized after partial purification. The isomerase was found to be enriched in preparations of an unrelated recombinant protein. Crystals of the isomerase were obtained from two different precipitants despite the fact that the recombinant protein represented roughly 90% of the total protein present. The crystals diffract to 2.7 A resolution and are suitable for a structure determination. The role of the isomerase in E. coli is uncertain, as E. coli is not known to degrade the polysaccharides which are potential sources of 5-keto-4-deoxyuronate.

Mitogen-activated protein kinases (Erk1,2) phosphorylate Lys-Ser-Pro (KSP) repeats in neurofilament proteins NF-H and NF-M

Mammalian neurofilament proteins, particularly midsized (NF-M) and heavy (NF-H) molecular weight neurofilament proteins, are highly phosphorylated in axons. Neurofilament function depends on the state of phosphorylation of the numerous serine/threonine residues in these proteins. Most phosphorylation occurs in the lys-ser-pro (KSP) repeats in the C-terminal tail domains of NF-H and NF-M. In our previous study, cyclin-dependent kinase 5 (cdk5) was shown to phosphorylate specifically the KSPXK repeats in rat NF-H. Because 80% of the repeats are of the KSPXXXK type, it was of interest to determine which kinase phosphorylates these motifs. Using a synthetic KSPXXXK peptide to screen for a specific kinase, we fractionated rat brain extracts by column chromatography and identified extracellular signal-regulated kinase (Erk2) activated by an upstream activator, the mitogen-activated protein kinase kinase MAPKK (MEK), by Western blot analysis, sequence identification, and inhibition by a specific MEK inhibitor (PD 98059). The fraction containing Erk2, as well as bacterially expressed Erk1 and Erk2, phosphorylated all types of KSP motifs in peptides (KSPXK, KSPXXK, KSPXXXK, and KSPXXXXK) derived from NF-M and NF-H. They also phosphorylated an expressed 24 KSPXXXK repeat NF-H polypeptide, an expressed NF-H as well as dephosphorylated native rat NF-H, and NF-M proteins with accompanying decreases in their respective electrophoretic mobilities. A comparative kinetic study of Erk2 and cdk5 phosphorylation of KSPXK and KSPXXXK peptides revealed that, in contrast to cdk5, which phosphorylated only the KSPXK peptide, Erk2 could phosphorylate both. The preferred substrate for Erk2 was KSPXXXK peptide. The MEK inhibitor PD 98059 also inhibited phosphorylation of NF-H, NF-M, and microtubule-associated protein (MAP) in primary rat hippocampal cells and caused a decrease in neurite outgrowth, suggesting that Erk1,2 may play an important role in neurite growth and branching. These data suggest that neuronal Erk1 and Erk2 are capable of phosphorylating serine residues in diverse KSP repeat motifs in NF-M and NF-H.

Site-specific phosphorylation of Lys-Ser-Pro repeat peptides from neurofilament H by cyclin-dependent kinase 5: structural basis for substrate recognition

Recent work has shown that high molecular weight neurofilament (NF) proteins are phosphorylated in their carboxy-terminal tail portion by the enzyme cyclin-dependent kinase 5 (CDK-5). The tail domain of neurofilaments contains 52 tripeptide repeats, viz. Lys-Ser-Pro, which mainly exist as KSPXK and KSPXXX motifs (X = amino acid). CDK-5 specifically phosphorylates the serine residues within the KSPXK sites. We probed the structural basis for this type of substrate selectivity by studying the conformation of synthetic peptides containing either KSPXK or KSPXXX repeats designed from native neurofilament sequences. Synthetic peptides with KSPXK repeats were phosphorylated on serine with a recombinant CDK-5/p25 complex whereas those with KSPXXX repeats were unreactive in this system. Circular dichroism (CD) studies in 50% TFE/H2O revealed a predominantly helical conformation for the KSPXXX-containing peptides, whereas the CD spectra for KSPXK-containing peptides indicated the presence of a high population of extended structures in water and 50% TFE solutions. However, detailed NMR analysis of one such peptide which included two such KSPXK repeats suggested a turn-like conformation encompassing the first KSPXK repeat. Restrained molecular dynamics calculations yielded an unusually stable, folded structure with a double "S"-like bend incorporating the central residues of the peptide. The data suggest that a transient reverse turn or loop-type structure may be a requirement for CDK-5-promoted phosphate transfer to neurofilament-specific peptide segments.

Characterization of the phosphorylation sites of human high molecular weight neurofilament protein by electrospray ionization tandem mass spectrometry and database searching

Hyperphosphorylated high molecular weight neurofilament protein (NF-H) exhibits extensive phosphorylation on lysine-serine-proline (KSP) repeats in the C-terminal domain of the molecule. Specific phosphorylation sites in human NF-H were identified by proteolytic digestion and analysis of the resulting digests by a combination of microbore liquid chromatography, electrospray ionization tandem (MS/MS) ion trap mass spectrometry, and database searching. The computer programs utilized (PEPSEARCH and SEQUEST) are capable of identifying peptides and phosphorylation sites from uninterpreted MS/MS spectra, and by use of these methods, 27 phosphopeptides and their phosphorylated residues were identified. On the basis of these phosphopeptides, 38 phosphorylation sites in human NF-H were characterized. These include 33 KSP, lysine-threonine-proline (KTP) or arginine-serine-proline (RSP) sites and four unphosphorylated sites, all of which occur in the KSP repeat domain (residues 502-823); and one threonine phosphorylation site observed in a KVPTPEK motif. Six KSP sites were not characterized because of the failure to isolate and identify corresponding phosphopeptides. Heterogeneity in serine and threonine phosphorylation was observed at three sites or deduced to occur at three sites on the basis of enzyme specificity. As a result of the phosphorylated motifs identified (KSPAKEE, KSPVKEE, KS/TPEKAK, KSPEKEE, KSPVKAE, KSPAEAK, KSPPEAK, KSPEAKT, KSPAEVK, and KVPTPEK), human NF-H tail domain is postulated to be a substrate of proline-directed kinases. The threonine-phosphorylated KVPTPEK motif suggested the existence of a novel proline-directed kinase.

Histone H1 isoforms purified from rat liver bind nonspecifically to the nuclear factor 1 recognition sequence and serve as generalized transcriptional repressors

Two polypeptides with molecular masses of 34 and 30 kDa were copurified from rat liver during DNA affinity purification of a sequence-specific transcription factor binding to the footprint II sequence within the P2 promoter of the rat alpha1B adrenergic receptor (alpha1B AR) gene, and were identified by microsequencing their endoproteinase Lys-C-derived peptides as histone H1d and histone H1c, respectively. Histone H1 was previously reported to bind to the nuclear factor 1 (NF1) recognition sequence, although the specificity of this binding has been controversial. Here, DNA mobility shift and supershift assays, DNase I footprinting and mutational analyses indicated that the binding of histone H1 to the NF1 sites located within footprint II of the alpha1B AR gene P2 promoter is nonspecific. Transient cotransfections into Hep3B cells of histone H1d cDNA with CAT constructs containing promoter regions of different genes resulted in generalized and non-specific suppression of CAT activity. The histone H1d-mediated repression of the activities of the alpha1B AR gene P2/CAT or beta2 AR gene P(-186/1307)/CAT constructs was reversed by the cotransfection of a cDNA encoding the sequence-specific transcription factor NF1/X, and the fold increase in CAT activities was similar to that obtained in the absence of histone H1d. These results suggest that sequence-specific transcription factors counteract the histone H1-mediated transcriptional repression in vivo by a true activation, which is different from the in vitro antirepression in histone H1-repressed chromatin templates (Laybourn and Kadonaga, (1991) Science 254: 238-245).

Risk factors for Kaposi's sarcoma in HIV-positive subjects in Uganda

BACKGROUND

Kaposi's sarcoma (KS) is associated epidemiologically with HIV infection and with human herpesvirus 8 (HHV-8 or KSHV). Both KS and HIV infection are common in Uganda. We conducted a case-control study of 458 HIV-seropositive. Ugandan adults with KS and 568 HIV-seropositive subjects without KS to examine risk factors for HIV-associated KS.

METHODS

We recruited newly diagnosed adult KS cases from five hospitals in Kampala, Uganda and controls from a large referral clinic for HIV infection at Mulago Hospital. All cases and controls were counselled and tested for HIV and answered an interviewer-administered questionnaire about their home, socio-economic conditions, lifestyle and sexual behaviour before they became ill. Only HIV-seropositive subjects were included in the analysis.

RESULTS

There were 295 males and 163 females with KS and 227 male and 341 female controls. Age distribution was similar but there was a higher proportion of cases (45%) than controls (29%) residing in rural regions of Uganda. KS cases were more likely than controls to have a higher level of education (X2 for trend, 4.8; P = 0.03), to have occupations associated with affluence [chi 2 for heterogeneity, 17.3 on 5 degrees of freedom (df); P = 0.004] and to come from larger settlements [adjusted odds ratio (OR) for settlements of > 1000 versus 10-99 houses, 1.8; 95% confidence interval (CI), 1.1-3.0]. Cases were more likely than controls to have high household income (chi 2 for trend, 32.6; P < 0.001) and other markers of urban or rural wealth such as owning several cows (chi 2 for trend, 9.5; P = 0.002). Cases were more likely to travel away from home (adjusted OR, 1.6; 95% CI, 1.1-2.3) and more likely to have spent increasing time in contact with water (chi 2 for trend, 12.3; P < 0.001). Few indices of sexual behaviour were related to risk of KS, including reported number of sexual partners. Cases were more likely than controls to be married to one rather than several spouses (adjusted OR, 1.6; 95% CI, 1.2-2.2) and to have reported a history of sexually transmitted diseases (STD) (adjusted OR, 1.6; 95% CI, 1.2-2.3).

CONCLUSIONS

Among HIV-infected subjects, KS cases are characterized by better education and greater affluence, compared with controls. Urban address, travel away from home, exposure to water, monogamous marriage and self-reported STD were also more frequent among KS cases than controls. The higher socio-economic status of persons with HIV and KS may be a marker for enhanced exposure to a possibly sexually transmitted agent, or for a delayed exposure to a childhood infection. The risk posed by exposure to water among KS cases requires further study.

High affinity binding and allosteric regulation of Escherichia coli glycogen phosphorylase by the histidine phosphocarrier protein, HPr

The histidine phosphocarrier protein (HPr) is an essential element in sugar transport by the bacterial phosphoenolpyruvate:sugar phosphotransferase system. Ligand fishing, using surface plasmon resonance, was used to show the binding of HPr to a nonphosphotransferase protein in extracts of Escherichia coli; the protein was subsequently identified as glycogen phosphorylase (GP). The high affinity (association constant approximately 10(8) M-1), species-specific interaction was also demonstrated in electrophoretic mobility shift experiments by polyacrylamide gel electrophoresis. Equilibrium ultracentrifugation analysis indicates that HPr allosterically regulates the oligomeric state of glycogen phosphorylase. HPr binding increases GP activity to 250% of the level in control assays. Kinetic analysis of coupled enzyme assays shows that the binding of HPr to GP causes a decrease in the Km for glycogen and an increase in the Vmax for phosphate, indicating a mixed type activation. The stimulatory effect of E. coli HPr on E. coli GP activity is species-specific, and the unphosphorylated form of HPr activates GP more than does the phosphorylated form. Replacement of specific amino acids in HPr results in reduced GP activation; HPr residues Arg-17, Lys-24, Lys-27, Lys-40, Ser-46, Gln-51, and Lys-72 were established to be important. This novel mechanism for the regulation of GP provides the first evidence directly linking E. coli HPr to the regulation of carbohydrate metabolism.

Identification of neuropeptides in the midgut of parasitized insects: FLRFamides as candidate paracrines

Parasitism of Manduca sexta (Lepidoptera: Sphingidae) larvae by the braconid wasp Cotesia congregata (Hymenoptera: Braconidae) leads to accumulation of peptides in host neurons and neurosecretory cells of the central nervous system (CNS) and neurons and endocrine/paracrine cells of the midgut. This accumulation has now facilitated the characterization of two new members of the FLRFamide family from midguts of parasitized larvae. The peptides, given the names F24 and F39, are 24 and 39 amino acids in length with the sequences VRDYPQLLDSGMKRQDVVHSFLRFamide and YAEAAGEQVPEYQALVRDYPQLLDSGMKRQDVVHSFLRFamide. The sequence of F24 is identical to the C-terminal 24 amino acids of F39. The C-terminal 10-mer of each is identical to a previously characterized decapeptide neurohormone (F10). This sequence is preceded by a potential processing site. In nonparasitized insects F39 was present at several-fold the amount of F24. In parasitized insects F24 and F39 accumulate in the middle and posterior regions of the midgut, which are enriched in endocrine/paracrine cells reacting with FLRFamide antisera. In the combined brain and subesophageal ganglion F39 was not detected and the amount of F24 never exceeded 2 fmol per Br/SEG. Of the three peptides, only F10 was found in the hemolymph. Thus, F24 and F39 may be intermediates in the biosynthesis of F10 and may themselves be released locally from endocrine/paracrine cells in the midgut epithelium.

Isolation and molecular cloning of wortmannin-sensitive bovine type III phosphatidylinositol 4-kinases

Agonist-sensitive phosphoinositide pools are maintained by recently-identified wortmannin (WT)-sensitive phosphatidylinositol (PI) 4-kinase(s) (Nakanishi, S., Catt, K. J., and Balla, T. (1995) Proc. Natl. Acad. Sci. U.S.A. 92, 5317-5321). Two loosely membrane-associated WT-sensitive type III PI 4-kinases were isolated from bovine adrenal cortex as [3H]WT-labeled 110- and 210-kDa proteins. Based on peptide sequences from the smaller enzyme, a 3. 9-kilobase pair (kb) cDNA with an open reading frame encoding a 90-kDa protein was isolated from a bovine brain cDNA library. Expression of this cDNA in COS-7 cells yielded a 110-kDa protein with WT-sensitive PI 4-kinase activity. Northern blot analysis of a human mRNA panel showed a single approximately 3.8-kb transcript. Peptide sequences obtained from the 210-kDa enzyme corresponded to those of a recently described rat 230-kDa PI 4-kinase. A 6.5-kb cDNA containing an open reading frame of 6129 nucleotides that encoded a 230-kDa protein, was isolated from brain cDNA. Northern blot analysis of human mRNA revealed a major 7.5-kb transcript. The molecular cloning of these novel WT-sensitive type III PI 4-kinases will allow detailed analysis of their signaling and other regulatory functions in mammalian cells.

The class III POU factor Brn-4 interacts with other class III POU factors and the heterogeneous nuclear ribonucleoprotein U

The class III POU proteins are expressed throughout the central nervous system, including the hypothalamus, where they are often co-localized. Presumably, these POU proteins (Brain-1, Brain-2, Brain-4 and SCIP) serve as transcriptional transactivators. That they are co-expressed in some neurons suggests that, if they were to form homomeric and heteromeric complexes with each other, depending on the particular combination, they might have different DNA-binding specificities and, thus, activate different genes. We used purified fusion proteins of the four class III POU proteins in far-western assays to show that the proteins can interact. We confirmed their interactions using a two-hybrid system. Both techniques indicate that the interaction occurs through the POU domain. The far-western technique also allowed us to identify a 120-kDa nuclear protein that interacts with Brain-4. Subsequent affinity purification and microsequencing identified the protein as the heterogeneous nuclear ribonucleoprotein U (hnRNP U). This result suggests another mechanism by which a POU protein can influence gene expression: by facilitating the processing of pre-mRNA whose transcription it has stimulated.

Determination of a native proteolytic site in myelin-associated glycoprotein

Myelin-associated glycoprotein (MAG) is a transmembrane structural protein that is thought to be involved in the formation and/or maintenance of the myelin sheath. MAG is proteolyzed at a discrete location near its transmembrane domain by a calcium activated myelin-associated cysteine protease in the central nervous system. The soluble proteolysis product, dMAG, can be found in the cerebrospinal fluid. The proteolysis of MAG may be involved in the molecular mechanism of demyelination, as the proteolytic degradation of myelin proteins has been observed in disease states. The site for the proteolysis of MAG to dMAG was identified. This was accomplished by developing a protocol for the purification of soluble dMAG and by protein sequencing of short peptides containing the carboxy-terminus of dMAG. The results from these experiments indicated that the native proteolytic site in MAG was located extracellularly and occurred between residues 512 (Ala) and 513 (Lys), with a large hydrophobic residue at the P2 position (Trp-511). This finding in turn indicated that the protease for which MAG was a substrate had cathepsin L-like activity. Cathepsin L-like activity in myelin was confirmed by peptidolysis experiments using known cathepsin L substrates. Additional experiments are in progress to determine the identity of this protease.

FliN is a major structural protein of the C-ring in the Salmonella typhimurium flagellar basal body

The Salmonella typhimurium FliN protein has been proposed to form a mutually interacting complex with FliG and FliM, the switch complex, that is required for flagellar morphogenesis and function. We have used affinity chromatography for purification of extended flagellar basal bodies sufficient for quantitative analysis of their protein composition. The belled, extended structure is predominantly comprised of the switch complex proteins; with FliN present in the most copies (111 +/- 13). This explains why single, missense fliN, fliG or fliM mutations, found in many non-motile strains, can alter the belled morphology. Cell lysates from these strains contained the wild-type complement of FliG, FliM and FliN; but the basal bodies lacked the outer, cytoplasmic(C)-ring of the bell and were separated by sedimentation from FliM and FliN. The amount of FliG present in basal bodies from wild-type and one such mutant, FliN100LP, was comparable. These data show that: (1) the mutations define a FliG and FliMFliN multiple contact interface important for motility. (2) FliG is responsible for the increased size of the membrane-embedded MS-ring complex of belled relative to acid-treated basal bodies. (3) FliN, together with FliM, account for most of the C-ring. As a major component of the C-ring, FliN is distinct from the other proteins implicated in axial flagellar protein export. Inner, cytoplasmic rod basal substructure, seen by negative-stain and quick-freeze replica electron microscopy, may gate such export. Lack of connectivity between the cytoplasmic rod and ring substructures places contacts between FliG and FliMFliN at the periphery of the basal body, proximal to the flagellar intramembrane ring particles. This topology is consistent with models where torque results from interaction of circumferential arrays of the switch complex proteins with the ring particles.

Purification and cloning of the GTP cyclohydrolase I feedback regulatory protein, GFRP

The activity of GTP cyclohydrolase I, the initial enzyme of the de novo pathway for biosynthesis of tetrahydrobiopterin, the cofactor required for aromatic amino acid hydroxylations and nitric oxide synthesis, is sensitive to end-product feedback inhibition by tetrahydrobiopterin. This inhibition by tetrahydrobiopterin is mediated by the GTP cyclohydrolase I feedback regulatory protein GFRP, previously named p35 (Harada, T., Kagamiyama, H., and Hatakeyama, K. (1993) Science 260, 1507-1510), and -phenylalanine specifically reverses the tetrahydrobiopterin-dependent inhibition. As a first step in the investigation of the physiological role of this unique mechanism of regulation, a convenient procedure has been developed to co-purify to homogeneity both GTP cyclohydrolase I and GFRP from rat liver. GTP cyclohydrolase I and GFRP exist in a complex which can be bound to a GTP-affinity column from which GTP cyclohydrolase I and GFRP are separately and selectively eluted. GFRP is dissociated from the GTP agarose-bound complex with 0.2 NaCl, a concentration of salt which also effectively blocks the tetrahydrobiopterin-dependent inhibitory activity of GFRP. GTP cyclohydrolase I is then eluted from the GTP-agarose column with GTP. Both GFRP and GTP cyclohydrolase I were then purified separately to near homogeneity by sequential high performance anion exchange and gel filtration chromatography. GFRP was found to have a native molecular mass of 20 kDa and consist of a homodimer of 9.5-kDa subunits. Based on peptide sequences obtained from purified GFRP, oligonucleotides were synthesized and used to clone a cDNA from a rat liver cDNA library by polymerase chain reaction-based methods. The cDNA contained an open reading frame that encoded a novel protein of 84 amino acids (calculated molecular mass 9665 daltons). This protein when expressed in Escherichia coli as a thioredoxin fusion protein had tetrahydrobiopterin-dependent GTP cyclohydrolase I inhibitory activity. Northern blot analysis indicated the presence of an 0.8-kilobase GFRP mRNA in most rat tissues, the amounts generally correlating with levels of GTP cyclohydrolase I and tetrahydrobiopterin. Thus, mRNA levels were relatively high in liver and kidney and somewhat lower in testis, heart, brain, and lung. These results suggest that GFRP is widely expressed and may play a role in regulating not only phenylalanine metabolism in the liver, but also the production of biogenic amine neurotransmitters as well as nitric oxide synthesis.

An axoplasmic myosin with a calmodulin-like light chain

Organelles in the axoplasm from the squid giant axon move along exogenous actin filaments toward their barbed ends. An approximately 235-kDa protein, the only band recognized by a pan-myosin antibody in Western blots of isolated axoplasmic organelles, has been previously proposed to be a motor for these movements. Here, we purify this approximately 235-kDa protein (p235) from axoplasm and demonstrate that it is a myosin, because it is recognized by a pan-myosin antibody and has an actin-activated Mg-ATPase activity per mg of protein 40-fold higher than that of axoplasm. By low-angle rotary shadowing, p235 differs from myosin II and it does not form bipolar filaments in low salt. The amino acid sequence of a 17-kDa protein that copurifies with p235 shows that it is a squid optic lobe calcium-binding protein, which is more similar by amino acid sequence to calmodulin (69% identity) than to the light chains of myosin II (33% identity). A polyclonal antibody to this light chain was raised by using a synthetic peptide representing the calcium binding domain least similar to calmodulin. We then cloned this light chain by reverse transcriptase-PCR and showed that this antibody recognizes the bacterially expressed protein but not brain calmodulin. In Western blots of sucrose gradient fractions, the 17-kDa protein is found in the organelle fraction, suggesting that it is a light chain of the p235 myosin that is also associated with organelles.

Semipreparative chromatographic method to purify the normal cellular isoform of the prion protein in nondenatured form

A fundamental step in the pathogenesis of spongiform encephalopathies (prion diseases) is the conversion of the cellular isoform of prion protein (PrPC) into the infectious form (scrapie isoform, PrPSc), apparently by a conformational mechanism. Comparison of the native secondary and tertiary structures of both proteins is essential to elucidate the molecular basis of this transformation. To obtain sufficient quantities of native-like PrPC, we have developed a semipreparative method to purify PrPC from hamster brains. PrPC was solubilized from purified synaptosomal and microsomal membranes by the nonionic detergent n-octyl- beta-glucopyranoside; the soluble fraction was loaded at pH 7.5 onto a semipreparative cation-exchange TSK-SP-5PW (HPLC) column. The fractions eluted by linear NaCl gradient and enriched for PrPC were sequentially purified using an immobilized ion-affinity HPLC column charged by Co2+, followed by wheat germ agglutinin (WGA)-affinity HPLC or size-exclusion HPLC (SE-HPLC) using a TSK G3000SW column. More than 95% purity was achieved after SE-HPLC as estimated by quantitative densitometry of the silver-stained SDS-PAGE gel; the recovery of total brain PrPC was >/=8%. The purified PrPC was a monomer with an intact N-terminus, and with a Stoke's radius of 26 A, corresponding to that expected from the molecular weight for a native protein. The presence of the native-like conformation was further verified by peptide mapping after limited trypsin proteolysis, and by the apparent unfolding in guanidine hydrochloride, as detected by SE-HPLC.