Identification of a determinant of epidermal growth factor receptor ligand-binding specificity using a truncated, high-affinity form of the ectodomain

Murine and human epidermal growth factor receptors (EGFRs) bind human EGF (hEGF), mouse EGF (mEGF), and human transforming growth factor alpha (hTGF-alpha) with high affinity despite the significant differences in the amino acid sequences of the ligands and the receptors. In contrast, the chicken EGFR can discriminate between mEGF (and hEGF) and hTGF-alpha and binds the EGFs with approximately 100-fold lower affinity. The regions responsible for this poor binding are known to be Arg(45) in hEGF and the L2 domain in the chicken EGFR. In this study we have produced a truncated form of the hEGFR ectodomain comprising residues 1-501 (sEGFR501), which, unlike the full-length hEGFR ectodomain (residues 1-621, sEGFR621), binds hEGF and hTGF-alpha with high affinity (K(D) = 13-21 and 35-40 nM, respectively). sEGFR501 was a competitive inhibitor of EGF-stimulated mitogenesis, being almost 10-fold more effective than the full-length EGFR ectodomain and three times more potent than the neutralizing anti-EGFR monoclonal antibody Mab528. Analytical ultracentrifugation showed that the primary EGF binding sites on sEGFR501 were saturated at an equimolar ratio of ligand and receptor, leading to the formation of a 2:2 EGF:sEGFR501 dimer complex. We have used sEGFR501 to generate three mutants with single position substitutions at Glu(367), Gly(441), or Glu(472) to Lys, the residue found in the corresponding positions in the chicken EGFR. All three mutants bound hTGF-alpha and were recognized by Mab528. However, mutant Gly(441)Lys showed markedly reduced binding to hEGF, implicating Gly(441), in the L2 domain, as part of the binding site that recognizes Arg(45) of hEGF.

The three dimensional structure of the type I insulin-like growth factor receptor

Ever since the discovery of insulin and its role in the regulation of glucose metabolism, there has been great interest in the molecule itself, the insulin-like growth factors (IGFs), and their receptors (IR and IGF-R). These receptors form a subfamily of tyrosine kinase receptors which are large, transmembrane proteins consisting of several structural domains. Their ectodomains have a similar arrangement of two homologous domains (L1 and L2) separated by a Cys rich region. The C-terminal half of their ectodomains consists of three fibronectin type 3 repeats, and an insert domain that contains the alpha-beta cleavage site. This review summarises the key developments in the understanding of the structure of this family of receptors and their relation to other multidomain proteins. Data presented will include multiple sequence analyses, single molecule electron microscope images of the IGF-1R, insulin receptor (IR), and IR-Fab complexes, and the three dimensional structure of the first three domains of the IGF-1R determined to 2.6 A resolution by x ray crystallography. The L domains each adopt a compact shape consisting of a single stranded, right handed beta-helix. The Cys rich region is composed of eight disulphide bonded modules, seven of which form a rod shaped domain with modules associated in an unusual manner.

High affinity insulin binding by soluble insulin receptor extracellular domain fused to a leucine zipper

Insulin receptors (IRs) that are truncated at the end of the ectodomain form dimers that bind insulin with different characteristics to wild type receptors. These soluble IRs have lowered affinity for insulin compared with full-length IR, and exhibit linear Scatchard plots in contrast to the curvilinear plots obtained with full-length IR, IR truncated at the C-terminus of the transmembrane region and IR ectodomains fused to the self-associating constant domains from Fc or lambda immunoglobulins. In this report, we have fused the IR ectodomain to the 33 residue leucine zipper from the transcriptional activator GCN4 of Saccharomyces cerevisiae. This fusion protein binds insulin with high affinity in a manner comparable to native receptor. The respective dissociation constants were Kd1 8.2 X 10(-11) M and Kd2 1.6 x 10(-8) M for hIRedZip and Kd1 5.7 x 10(-11) M and Kd2 6.3 x 10(-9) M for membrane-anchored, native receptor.

Mutational analysis of the N-linked glycosylation sites of the human insulin receptor

Site-directed mutagenesis has been used to remove 15 of the 18 potential N-linked glycosylation sites, in 16 combinations, from the human exon 11-minus receptor isoform. The three glycosylation sites not mutated were asparagine residues 25, 397 and 894, which are known to be important in receptor biosynthesis or function. The effects of these mutations on proreceptor processing into alpha and beta subunits, cell-surface expression, insulin binding and receptor autophosphorylation were assessed in Chinese hamster ovary cells. The double mutants 16+78, 16+111, 16+215, 16+255, 337+418, the triple mutants 295+337+418, 295+418+514, 337+418+514 and 730+743+881 and the quadruple mutants 606+730+743+881 and 671+730+743+881 seemed normal by all criteria examined. The triple mutant 16+215+255 showed only low levels of correctly processed receptor on the cell surface, this processed receptor being autophosphorylated in response to insulin. The quadruple mutant 624+730+743+881 showed normal processing and ligand binding but exhibited a constitutively active tyrosine kinase as judged by autophosphorylation. Three higher-order mutants were constructed, two of which, 16+337+418+730+743+881 (Delta6) and 16+295+337+418+730+743+881 (Delta7a), seemed normal. The third construct, 16+337+418+514+730+743+881 (Delta7b), was expressed at high levels on the cell surface, essentially as uncleaved proreceptor with only the small proportion of Delta7b that was correctly processed showing insulin-stimulated autophosphorylation. The mutations of Delta6 and Delta7a were incorporated into soluble ectodomains, which had affinities for insulin that were 4-fold that of wild-type ectodomain. The Delta6 ectodomain expressed in Lec8 cells was produced in quantity in a bioreactor for subsequent structural analysis.

Properties of an insulin receptor with an IGF-1 receptor loop exchange in the cysteine-rich region

The insulin receptor (IR) and the insulin-like growth factor-I receptor (IGF-1R) show differential binding of insulin and IGFs. The specificity determinants for IGF-1 binding are known to be located in the cysteine-rich (Cys-rich) region between residues 223 and 274 of human IGF-1R, which includes a loop that protrudes into the putative ligand binding site. In this report we have replaced residues 260-277 of human IR with residues 253-266 of the human IGF-1R to produce an IR-based, cysteine loop exchange chimaera, termed hIR-Cys loop exchange (CLX), in which all 14 amino acid residues in the exchanged loop differ from wild-type insulin receptor. This loop exchange had a detrimental effect on the efficiency of pro-receptor processing and on the binding of the mouse monoclonal antibody 83-7. However, this antibody, which binds hIR but not hIGF-1R, was still capable of immunoprecipitating the mature chimaeric receptor, indicating that the conformational epitope recognised by this antibody is not primarily determined by the loop region exchanged. The loop exchange did not significantly affect the ability of insulin to displace bound radiolabelled insulin, but increased the capacity of IGF-1 to competitively displace labelled insulin by at least 10 fold.

Crystal structure of the first three domains of the type-1 insulin-like growth factor receptor

The type-1 insulin-like growth-factor receptor (IGF-1R) and insulin receptor (IR) are closely related members of the tyrosine-kinase receptor superfamily. IR is essential for glucose homeostasis, whereas IGF-1R is involved in both normal growth and development and malignant transformation. Homologues of these receptors are found in animals as simple as cnidarians. The epidermal growth-factor receptor (EGFR) family is closely related to the IR family and has significant sequence identity to the extracellular portion we describe here. We now present the structure of the first three domains of IGF-IR (L1-Cys-rich-L2) determined to 2.6 A resolution. The L domains each consist of a single-stranded right-handed beta-helix. The Cys-rich region is composed of eight disulphide-bonded modules, seven of which form a rod-shaped domain with modules associated in an unusual manner. The three domains surround a central space of sufficient size to accommodate a ligand molecule. Although the fragment (residues 1-462) does not bind ligand, many of the determinants responsible for hormone binding and ligand specificity map to this central site. This structure therefore shows how the IR subfamily might interact with their ligands.

Crystallization of the first three domains of the human insulin-like growth factor-1 receptor

The insulin-like growth factor-1 receptor (IGF-1R) is a tyrosine kinase receptor of central importance in cell proliferation. A fragment (residues 1-462) comprising the L1-cysteine rich-L2 domains of the human IGF-1R ectodomain has been overexpressed in glycosylation-deficient Lec8 cells and has been affinity-purified via a c-myc tag followed by gel filtration. The fragment was recognized by two anti-IGF-1R monoclonal antibodies, 24-31 and 24-60, but showed no detectable binding of IGF-1 or IGF-2. Isocratic elution of IGF-1R/462 on anion-exchange chromatography reduced sample heterogeneity, permitting the production of crystals that diffracted to 2.6 A resolution with cell dimensions a = 77.0 A, b = 99.5 A, c = 120.1 A, and space group P2(1)2(1)2(1).

Characterization of pilin genes from seven serologically defined prototype strains of Moraxella bovis

Numerous field isolates of Moraxella bovis have previously been classified by serological techniques into seven serogroups, each defined by homologous cross-reaction with antisera prepared against purified pili of a single prototype strain. The gene encoding pilin from each of the prototype strains has been characterized by nucleotide sequence determination. The coding sequences show extensive homology (70 to 80%) while the proximal downstream sequences show a dichotomy into nonhomologous sets. The pilin genes of three more strains were also characterized. The presence of an additional, partial pilin gene in each prototype strain was confirmed by Southern blot analysis, and the partial pilin genes from two strains of one serogroup were characterized by sequence determination. Features of the pilin gene sequences are considered in relation to pilin gene inversion and the serological variants of strains which may arise from gene inversion events.

A Moraxella bovis pili vaccine produced by recombinant DNA technology for the prevention of infectious bovine keratoconjunctivitis

Pili (fimbriae) were prepared from Moraxella bovis strain Dalton 2d (Dal2d) and from a derivative of Pseudomonas aeruginosa K/2PfS that contained a plasmid-borne Dal2d pilin gene and produced pili having serogroup-specific identity to Dal2d. Nine calves were vaccinated with two doses each of 30 micrograms authentic M. bovis Dal2d pili in oil adjuvant and 10 calves were vaccinated with a similar dose of P. aeruginosa-derived Dal2d pili in the same formulation. All 19 calves and 10 non-vaccinated controls were challenged by instillation of 1 x 10(9) virulent M. bovis Dal2d cells into both conjunctival sacs 19 days after the second vaccine dose. The serological response to vaccination and the degree of protection against experimentally induced infectious bovine keratoconjunctivitis (IBK) were assessed. None of the nine calves vaccinated with authentic M. bovis Dal2d pili developed IBK while two of those vaccinated with P. aeruginosa-derived Dal2d pili developed lesions which accounted for a mean group lesion score of 0.3. In contrast, 9 of the 10 non-vaccinated calves developed IBK lesions, the majority of which were progressive, required early treatment and accounted for a mean group lesion score of 1.5. These results demonstrate the potential of a relatively low dose of pili produced by recombinant DNA technology for development of an effective vaccine against IBK.

The effects of antigenic competition on the efficacy of multivalent footrot vaccines

A multivalent footrot vaccine has been developed, containing pilus antigens produced in recombinant Pseudomonas aeruginosa and representing all nine serogroups of Dichelobacter (Bacteroides) nodosus commonly recognised in the field. The responses of sheep to the multivalent vaccine have been compared with those to monovalent vaccines representing only a single serogroup. Antigenic competition between serogroups occurred in sheep immunised with the multivalent formation, but high levels of protection were still achieved. The study showed that in multivalent footrot vaccines, antigenic competition is predominantly due to the presence of a family of immunologically-related pilus antigens rather than to interference by extraneous proteins.

Production of Neisseria gonorrhoeae pili (fimbriae) in Pseudomonas aeruginosa

Pseudomonas aeruginosa K/2PfS, when transformed with an expression plasmid harboring the pilin gene (pilE1) of Neisseria gonorrhoeae MS11, was able to express and assemble gonococcal pilin monomers into surface-associated pili, as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, immunoblotting, and immunoelectron microscopy. Concomitant with the expression of gonococcal pili in P. aeruginosa was the virtual loss of production of P. aeruginosa K/2PfS pili normally associated with the host cell.

Cross-protective immunity and the serological classification system for Bacteroides nodosus

The relationship between the serological classification system for serogroup B and for serogroup H of Bacteroides nodosus and cross-protection between subgroups within these serogroups was examined. Protection against ovine footrot following vaccination was achieved against other subgroup strains provided sufficient cross-reactive antibody was induced by shared pilus antigens. Within serogroup B, better cross-protection against one subgroup was obtained with a pili vaccine than a whole cell vaccine which correlated with higher pilus antibody titres induced by the former. For serogroup H, a lack of cross-protection and serological reactivity between subgroups was demonstrated, which indicates that the prototype strain of subgroup H2 should be designated a new serogroup.

Pilins from the B serogroup of Bacteroides nodosus: characterization, expression, and cross-protection

Sequences of pilin genes from four strains of serogroup B of the ovine pathogen Bacteroides nodosus have been determined. These sequences permit comparisons of amino acid sequence between pilins from different subtypes (B1, B2, B3, B4) of the B serogroup and assessment of intraserogroup variation. Pili of B. nodosus strains 234 (B1) and 183 (B2) were produced by Pseudomonas aeruginosa harboring a plasmid-borne B. nodosus pilin gene, and these pili were used in sheep vaccination trials. Pili from strain 183 (B2) were found to be a senior antigen to pili from strains of other B subtypes, providing protection against footrot infection caused by strains of the other B subtypes. Pili of this strain are therefore the most suitable candidate for inclusion in a pilus-based vaccine. Pili of strain 234 from subtype B1, the reference strain of the B serogroup, provided poor protection against infection with other subtypes.

Characterization of the pilin gene of Moraxella bovis Dalton 2d and expression of pili from M. bovis in Pseudomonas aeruginosa

The pilin gene of Moraxella bovis Dalton 2d was isolated by cloning in Pseudomonas aeruginosa. The nucleotide sequence of this gene encodes a prepilin of 156 amino acid residues. When high levels of pilin were expressed from the gene in P. aeruginosa, by using the pL promoter of bacteriophage lambda inserted upstream of the coding sequence, pili which were indistinguishable from pili of M. bovis were produced.

Sequence of pilin from Bacteroides nodosus 351 (Serogroup H) and implications for serogroup classification

The nucleotide sequence of the pilin gene from Bacteroides nodosus strain 351, currently classified as serogroup H, subgroup 2 (H2) has been determined. The gene encodes a single polypeptide (prepilin) of 160 amino acids and Mr 17,150. However, pilin isolated from B. nodosus 351 migrates as two distinct bands in sodium dodecyl sulphate-polyacrylamide gel electrophoresis, due to an internal peptide bond cleavage. Amino acid sequence studies of pilin from B. nodosus 351 have established that the cleavage occurs between 72Ala and 73Ser of the mature protein sequence. Comparisons of gene and amino acid sequences of pilin from B. nodosus 351 with the corresponding sequences from strains of serogroups D and H1 indicate that these sequences share a close relationship. However, the level of sequence identity between B. nodosus 351 pilin and pilin from strain 265 of serogroup H1 is lower than anticipated for strains within a serogroup and suggests that B. nodosus 265 and B. nodosus 351 should not be classified within the same serogroup.

Pilins of Bacteroides nodosus: molecular basis of serotypic variation and relationships to other bacterial pilins

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Nucleotide sequence of the pilin gene of Bacteroides nodosus 340 (serogroup D) and implications for the relatedness of serogroups

The gene encoding pilin of Bacteroides nodosus 340 has been isolated and the nucleotide sequence determined. The gene is present as a single copy within the B. nodosus genome and a protein of Mr 16683 can be predicted from the proposed coding region. A comparison of the predicted amino acid sequence with pilin from other strains of B. nodosus indicated that the protein of strain 340 (serogroup D) has a high degree of similarity with pilin of strain 265 (serogroup H). The degree of similarity between pilins from these strains and from other B. nodosus serogroups is no greater than that between B. nodosus pilins and the homologous proteins of several different bacterial species. These findings suggest that serogroups D and H may form a subset of B. nodosus serogroups.

Efficacy against footrot of a Bacteroides nodosus 265 (serogroup H) pilus vaccine expressed in Pseudomonas aeruginosa

Pili of Bacteroides nodosus 265 (serogroup H) were expressed in Pseudomonas aeruginosa both alone and in combination with pili from B. nodosus 198 (serogroup A). Pilin genes from B. nodosus were introduced on plasmid-borne, thermoregulated expression systems, either singly or as tandem genes from two separate strains in a single transcription unit. Despite the absence of a posttranslational cleavage of pilin which occurs in B. nodosus, pili prepared from P. aeruginosa harboring the pilin gene of B. nodosus 265 protected sheep against footrot after challenge by B. nodosus 265. Organisms harboring pilin genes from the two different serogroups of B. nodosus produced serologically distinct populations of pili on each cell, and pili from these cells protected sheep against footrot after challenges with B. nodosus strains 198 and 265.

Expression of multiple types of N-methyl Phe pili in Pseudomonas aeruginosa

The nature of pili synthesized by Pseudomonas aeruginosa when plasmid-borne genes of homologous pilins from Bacteroides nodosus are introduced as thermoregulated expression systems has been ascertained. Expression of B. nodosus pili inhibited the production of indigenous P. aeruginosa pili, and an organism harbouring pilin genes from two strains of B. nodosus produced two serologically distinct populations of pili on each cell. Simultaneous production of both indigenous and foreign pili was achieved by partial induction of expression. Homogeneity in pilus structure suggests either that there is an exclusive specificity of interaction between identical pilin subunits in pilus assembly, or that each pilus is produced from the translation products of a single messenger RNA molecule, with translation and pilus assembly closely coupled.

Expression of pili from Bacteroides nodosus in Pseudomonas aeruginosa

The pili of Bacteroides nodosus, the causative agent of ovine footrot, constitute the major host-protective immunogen against homologous serotypic challenge. The pilin gene from B. nodosus 198 has been cloned and morphologically expressed as extracellular pili in Pseudomonas aeruginosa by using a plasmid-borne, thermoregulated expression system. B. nodosus pilin could not be detected in cultures of P. aeruginosa grown at 32 degrees C, but after induction at 37 degrees C, B. nodosus pili were expressed on the cell surface of P. aeruginosa to the virtual exclusion of the host cell pili. Pili harvested from induced P. aeruginosa cultures were used to immunize sheep against footrot. The serum agglutinating antibody titers of vaccinated sheep were comparable to those of sheep receiving pili from B. nodosus. Subsequent challenge of the sheep with B. nodosus 198 indicated that the recombinant- DNA-derived pili vaccine and the B. nodosus pili vaccine provided similar levels of protection against footrot.

Nucleotide sequence of the gene encoding the two-subunit pilin of Bacteroides nodosus 265

The nucleotide sequence of the gene encoding pilin from Bacteroides nodosus 265 has been determined. The pilin is encoded by a single-copy gene, from which can be predicted a prepilin comprising a single protein chain of Mr 16,637. The prepilin sequence differs in several respects from the mature protein sequence. Seven additional N-terminal amino acid residues are present in prepilin, whereas residue 8, phenylalanine, undergoes posttranslational modification to become the N-methylated amino-terminal residue of mature pilin. In addition, further processing occurs through internal cleavage to produce two noncovalently linked subunits characteristic of pilins from serogroup H of B. nodosus, of which strain 265 is a member. The position of cleavage has been identified between alanine residues at positions 72 and 73 of the mature 149-residue pilin protein. The predicted pilin sequence of B. nodosus 265 shows extensive N-terminal amino acid sequence homology with other pilins of the N-methylphenylalanine type. In addition this sequence also shows homology with these N-methylphenylalanine-type pilins in the C-terminal region of the molecule, especially with pilin from Pseudomonas aeruginosa PAK.

Expression of the pilin gene from Bacteroides nodosus in Escherichia coli

Bacterial plasmids that direct the expression in Escherichia coli of the pilin of Bacteroides nodosus were constructed. The quantity of pilin produced was greater than that of the pilin synthesized by B. nodosus, but no surface structural pili were present; pilin was found associated with the inner membrane of E. coli. Vaccination of sheep with E. coli containing pilin elicited increases in agglutinating and enzyme-linked immunosorbent assay antibody titers, which in turn were lower than the titers in sheep immunized with pilin from B. nodosus. The E. coli-produced pilin vaccine initially appeared to delay the progression of infection in immunized sheep after a challenge with virulent homologous B. nodosus, but at a later time the severity of foot rot was similar to that in sheep vaccinated with a placebo.

Nucleotide sequence of the gene encoding pilin of Bacteroides nodosus, the causal organism of ovine footrot

The nucleotide sequence encoding pilin, the monomer protein subunit of the pilus from Bacteroides nodosus, has been determined. The sequence predicts a short, positively charged, amino-terminal segment which is absent from the amino acid sequence of mature pilin. The coding sequence is preceded upstream by a sequence of five nucleotides complementary to the 3' end of 16S rRNA of Escherichia coli--a potentially good ribosome binding site--and even further upstream by an AT-rich region preceding several potential recognition sites for RNA polymerase. The coding sequence is followed by a region of hyphenated dyad symmetry having the potential to act as a rho-independent terminator of transcription.

Isolation of the gene encoding pilin of Bacteroides nodosus (strain 198), the causal organism of ovine footrot

The gene for pilin, the monomeric protein subunit from which the pilus of Bacteroides nodosus is constructed, has been isolated. Isolation was achieved by cloning the fragmented genome of B. nodosus in Escherichia coli RR1 using the plasmid vector pBR322. Pilin-producing colonies were identified by screening with a colony immunoassay using antiserum from a sheep immunized against purified pili from B. nodosus strain 198, and were further characterized by immunoblot analysis. Final confirmation of the presence of the pilin gene was by nucleotide sequence data which translated to the known pilin amino acid sequence.

Nucleotide sequence of gene segment 9 encoding a nonstructural protein of UK bovine rotavirus

A full-length ds cDNA copy of UK bovine rotavirus gene segment 9, which codes for a nonstructural protein, has been cloned into the PstI site of pBR322, and its sequence has been determined by cloning into bacteriophage M13mp8. Gene 9 is 1076 nucleotides long and contains a single, long, open-reading frame capable of coding for a protein of 313 amino acid residues. The possible function of this nonstructural protein in virus replication is discussed.

Nucleotide sequence of the gene encoding the serotype-specific glycoprotein of UK bovine rotavirus

The nucleotide sequence of the gene which encodes the major outer-shell glycoprotein of UK bovine rotavirus has been determined. The dsRNA genome segment encoding this protein was converted into ds cDNA and cloned into pBR322 for sequence studies. The gene is 1062 base pairs in length and contains a single, long, open reading-frame capable of coding for a protein of 326 amino-acids. This would leave 5' and 3' non-coding regions of 48 and 36 nucleotides in the mRNA. The predicted amino-acid sequence contains three possible glycosylation sites of the type Asn-X-Ser Thr, and an extremely hydrophobic N-terminal region. This sequence is discussed in the light of the known properties and functions of the protein.

Cloning and sequence of UK bovine rotavirus gene segment 7: marked sequence homology with simian rotavirus gene segment 8

The genome of the UK bovine rotavirus, which consists of eleven segments of dsRNA was polyadenylated and reverse-transcribed into cDNA. Complementary cDNA strands were annealed and the termini of the duplexes completed using DNA polymerase I. Full-length DNA copies of RNA segments 7, 8 and 9 were cloned into the Pst I site of pBR322 and a clone containing the entire gene 7 was identified and sequenced. Gene 7 is 1059 nucleotides in length and contains a single long open reading frame capable of coding for a protein of 317 amino-acids. The known gene product of segment 7 is a protein with an estimated molecular weight of 33,000 daltons. When the UK bovine rotavirus gene 7 sequence was compared with the published data for the homologous gene (segment 8) of the simian rotavirus SA11, it was found to be identical to it in size and the arrangement of the proposed coding and non-coding regions, and very similar in nucleotide sequence (88% homology). Most of the base changes are silent and the predicted amino-acid sequences are almost identical (96% homology).

Neuraminidase gene from the early Asian strain of human influenza virus, A/RI/5-/57 (H2N2)

The complete structure of the neuraminidase gene from the A/RI/5-/57 strain of influenza virus has been determined. It is 1467 nucleotides long and codes for a protein of 469 amino acid residues. Comparison with the gene sequence for the N1 strains A/WSN/33 and A/PR/8/34, the N2 strain A/Udorn/72 and the protein sequence for the N2 strain A/Tokyo/3/67 shows the amino acid sequence changes that have occurred during antigenic shift (60%) and drift (7-9%).

Amino acid sequence of the Pronase-released heads of neuraminidase subtype N2 from the Asian strain A/Tokyo/3/67 of influenza virus

The amino acid sequence of the Pronase-released heads of neuraminidase subtype N2 from the A/Tokyo/3/67 strain of influenza virus was determined by a combination of peptide and nucleic acid sequence analysis. The results show that the Pronase-released heads contain 396 amino acid residues and extend from residue 74 in the original protein to the C-terminus at residue 469. The heads contain five potential glycosylation sites at asparagine residues 86, 146, 200, 234 and 402, but only the first four are glycosylated. The sequence homology with the corresponding region of the previously published sequence of the neuraminidase subtype N1 [Fields, Winter & Brownlee (1981) Nature (London) 290, 213-217] is 45%. Detailed evidence for the sequence data has been deposited as Supplementary Publication SUP 50116 (14 pages) at the British Library Lending Division, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies may be obtained on the terms given in Biochem. J. (1981) 193, 5.

The primary structure of hen ovotransferrin

Peptide sequences obtained from hen ovotransferrin are compared with the complete amino acid sequence of the protein deduced from a cDNA sequence (Jeltsch and Chambon, preceding paper). Of the 705 positions of the whole protein 605 can be matched by the peptide sequences. Some possible discrepancies between the two methods are pointed out. The two halves of the chain show marked similarities in their sequences with 37% identical residues. The positions of the 15 disulphide bridges are shown; there are 6 homologous bridges in each half of the molecule and 3 extra bridges which occur only in the C-terminal half. The terminal residues of the half-molecule fragments obtained by limited proteolysis are identified. The two domains are joined by a 9-residue connecting peptide. Sequence variability has been found at 9 positions. The sequence of hen ovotransferrin is compared with the partial available for human transferrin. From this some tentative conclusions about the identities of the metal-binding residues and about the evolution of transferrin are reached.

Sequence of 863 nucleotides encompassing the PstI site of the yeast 2 micron plasmid

The sequence of part of the larger unique region of the yeast 2 micron plasmid cloned in pMB9 has been determined. The sequence extends from the single EcoRI site in this region to the AvaI site and includes the single PstI site and HpaI site. A notable feature of this sequence is the presence of tandem repeats of 124 residues beginning at the HpaI site and extending beyond the AvaI site. The sequence was determined independently by both the Maxam-Gilbert procedure applied to isolated restriction fragments, and by the chain-termination procedure applied to restriction fragments cloned in the single-stranded phage M13mp2 and purified by plaque selection.

Amino acid sequences of alpha-helical segments from S-carboxymethylkerateine-A. Statistical analysis

The distribution of the different types of amino acid residue within two helical segments isolated from the low-sulphur fraction of wool keratin was examined for periodicity and larger sequence repeats. Both were detected, the former corresponding to the geometry of the proposed coiled=coil structure and the latter suggesting a distant gene duplication, though the existence of the repeat might equally well be related to interactions within the microfibril.

A method for detecting distant evolutionary relationships between protein or nucleic acid sequences in the presence of deletions or insertions

A method for detecting homology between two protein or nucleic acid sequences which require insertions or deletions for optimum alignment has been devised for use with a computer. Sequences are assessed for possible relationship by Monte Carlo methods involving comparisons between the alignment of the real sequences and alignments of randomly scrambled sequences of the same composition as the real sequences, each alignment having the optimum number of gaps. As each gap is successively introduced into a comparison (real or random) a maximum score is determined from the similarity of the aligned residues. From the distribution of the maximum alignment scores of randomly scrambled sequences having the same number of gaps, the percentage of random comparisons having higher scores is determined, and the smallest of these percentage levels for each pair of sequences (real or random) indicates the optimum alignment. The fraction of the comparisons of random sequences having percentage levels at their optimum alignment below that of the real sequence comparison at its optimum estimates the probability that such an alignment might have arisen by chance. Related sequences are detected since their optimum alignment score, by virtue of a contribution from ancestral homology in addition to optimised random considerations, occupies a more extreme position in the appropriate frequency distribution of score than do the majority of optimum scores of randomly scrambled sequences in their appropriate distributions. Application of this 'optimum match' method of sequence comparison shows that the sensitivity of the 'maximum match' method of Needleman and Wunsch (1970) decreases quite dramatically with sequence comparisons which require only a few gaps for a reasonable alignment, or when sequences differ greatly in length. The 'maximum match' method as applied by Barker and Dayhoff (1972) has the additional disadvantage that deletions which have occurred in the longer of two homologous protein sequences further decrease the sensitivity of detection of relationship. The 'constrained match' method of Sankoff and Cedergren (1973) is seen to be misleading since large increments in the alignment score from added gaps do not necessarily result in a high total alignment score required to demonstrate sequence homology.

Isolation, characterization and pathology of the toxin from a Microcystis aeruginosa (= Anacystis cyanea) bloom

The nature of the toxicity of a bloom of blue-green alga, M. aeruginosa (= Anacystis cyanea), that occurred in a man-made lake was investigated. Crude algal bloom extracts were toxic to laboratory mice when injected intraperitoneally. The lethal dose (LD100) of these extracts was 15-30 mg of lyophilized algal bloom per kilogram body weight. The toxin was purified by a procedure that included ammonium sulphate fractionation, solvent extraction, acid precipitation, Sephadex G25 and DEAE-Sephadex chromatography, and high-voltage electrophoresis at pH 6.5. The preparation gave a single spot on high-voltage electrophoresis at pH 9.0, had no free amino group, and was characterized by a simple amino acid composition of equimolar quantities of L-methionine, L-tyrosine, D-alanine, D-glutamic acid, erythro beta-methyl aspartic acid and methylamine. The LD50 for the purified toxin was estimated to be 0.056 mg/kg of mice, and the approximate LD100 is 0.070 mg/kg, based on the total material found from amino acid analysis. Parenteral administration of the purified toxin to mice produced extensive liver lobular haemorrhage and death within 1-3 h. Repeated inoculation of sublethal doses daily over some weeks produced progressive hepatocyte degeneration and necrosis and the development of fine hepatic fibrosis.

Amino acid sequence of the smaller subunit of conglutin gamma, a storage globulin of Lupinus angustifolius

The amino acid sequence of the smaller subunit of conglutin gamma, the simplest of the three globulins from the seeds of Lupinus angustifolius cv. Uniwhite, has been determined. The subunit was homogeneous and contained 154 amino acid residues, including five sulphur-containing amino acids--a considerably higher content than is found in most other legume storage proteins. There was no indication of the complexity experienced in studies of many other legume storage proteins. This is perhaps the first sequence of a subunit of a legume storage protein to be determined.

Amino Acid Sequence of the Smaller Subunit of Conglutin ?, a Storage Globulin of Lupinus angustifolius

The amino acid sequence of the smaller subunit of conglutin y, the simplest of the three globulins from the seeds of Lupinus angusti/olius cv. Uniwhite, has been determined. The subunit was homogeneous and contained 154 amino acid residues, including five sulphur-containing amino acids-a considerably higher content than is found in most other legume storage proteins. There was no indication of the complexity experienced in studies of many other legume storage proteins. This is perhaps the first sequence of a subunit of a legume storage protein to be determined.

Aminopeptides of pea

Studies of crude extracts of pea seeds (Pisum sativum, var. Green feast) revealed the presence of three enzymes that hydrolyse the amide bond of aminoacyl beta-naphthylamides. They differ in their specificity towards the aminoacyl moiety; one is proline-specific, whereas the other two hydrolyse the beta-naphthylamides of primary amino acids. Of the latter, one is highly specific for hydrophobic aminoacyl residues whereas the other has a broader, somewhat complementary specificity, showing preferential hydrolysis of non-hydrophobic aminoacyl residues. These latter two aminoacyl-beta-naphthylamidases have been separated and partly characterized with regard to substrate specificity and antagonism by inhibitors. Both are true aminopeptidases, requiring the presence of a free amino group and hydrolysing the amide bonds of amino acid amides, dipeptides and oligopeptides consecutively from the N-terminal end.

The amino acid sequence of protein SCMK-B2A from the high-sulphur fraction of wool keratin

1. The amino acid sequence of protein SCMK-B2A, a reduced and S-carboxymethylated protein from the high-sulphur fraction of wool, has been determined. 2. This protein of 171 amino acid residues displays both a high degree of internal homology and extensive external homology with other members of the SCMK-B2 group of proteins. 3. Evidence is presented which suggests that the SCMK-B2 group of proteins are produced by separate non-allelic genes.

The amino acid sequence of protein SCMK-B2C from the high-sulphur fraction of wool keratin

1. The amino acid sequence of a protein from the reduced and carboxymethylated high-sulphur fraction of wool has been determined. 2. The sequence of this S-carboxymethylkerateine (SCMK-B2C) of 151 amino acid residues displays much internal homology and an unusual residue distribution. Thus a ten-residue sequence occurs four times near the N-terminus and five times near the C-terminus with few changes. These regions contain much of the molecule's half-cystine, whereas between them there is a region of 19 residues that are mainly small and devoid of cystine and proline. 3. Certain models of the wool fibre based on its mechanical and physical properties propose a matrix of small compact globular units linked together to form beaded chains. The unusual distribution of the component residues of protein SCMK-B2C suggests structures in the wool-fibre matrix compatible with certain features of the proposed models.

The preparation and properties of a group of proteins from the high-sulphur fraction of wool

A method is reported for the preparation of a group of three proteins from the S-carboxymethylated high-sulphur fraction of wool. These proteins have been partially characterized by their tryptic peptides. All have similar structural features and show an interesting homology within the group and some similarities of sequence with a different group of wool high-sulphur proteins. The evidence for the sequence of some of the peptides is given in a supplementary paper that has been deposited as Supplementary Publication 50008 at the National Lending Library for Science and Technology, Boston Spa, Yorks. LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1972) 126, 5.

The amino acid sequences of cysteic acid-containing peptides from performic acid-oxidized ovotransferrin

1. The half-cystine content of ovotransferrin, measured as cysteic acid, was 31mol/80000g of protein. 2. The amino acid sequences of cysteic acid-containing peptides from performic acid-oxidized ovotransferrin were studied. 3. 34 unique cysteic acid residues were identified. 4. It is concluded that hen ovotransferrin does not consist of two identical halves or subunits.