Structural difference between the normal PiM1 and the common PiM2 variant of human alpha 1-antitrypsin.

The common PiM2 variant of human alpha 1-antitrypsin (alpha 1-AT) which can be distinguished from the wild type PiM1 by isoelectric focusing (IEF) in a narrow pH gradient, was purified to homogeneity from plasma of a homozygous PiM2/PiM2 subject. The specific trypsin inhibitory activity and the amino acid and carbohydrate composition of the normal PiM1 and the variant PiM2 are very similar. The structural difference between the normal and the variant inhibitors was elucidated by peptide mapping of their tryptic digests. An amino acid substitution of glutamic acid in the normal inhibitor by aspartic acid in the variant inhibitor was found. The same amino acid substitution was found in PiMN, which was presumed to be identical to PiM2 based on their IEF patterns.     

Molecular abnormality of PI S variant of human alpha1-antitrypsin.

Alpha1-antitrypsin variant protein was purified to homogeneity from a PI S-S subject with a mild deficiency of plasma trypsin inhibiting capacity. Molecular weight, specific trypsin inhibitory activity, and composition of amino acids and carbohydrates were similar to the proteins purified from Pi M-M individuals with normal alpha1-antitrypsin activity. The structural difference between the normal and the variant alpha1-antitrypsin was elucidated by peptide mapping of their tryptic digests. An amino acid substitution of glutamic acid in the normal protein to valine in the variant protein was found. The result is consistent with the previously reported amino acid substitution in Pi S-Christchurch.     

Mutations in Hemagglutinin and Polymerase Alter the Virulence of Pandemic A(H1N1) Influenza Virus

To study the pathogenicity factors of the pandemic A(H1N1) influenza virus, a number of mutant variants of the A/Hamburg/5/2009 (H1N1)pdm09 strain were obtained through passage in chicken embryos, mouse lungs, and MDCK cell culture. After 17 lung-to-lung passages of the A/Hamburg/5/2009 in mice, the minimum lethal dose of the derived variant decreased by five orders of magnitude compared to that of the parental virus. This variant differed from the original virus by nine amino acid residues in the following viral proteins: hemagglutinin (HA), neuraminidase (NA), and components of the polymerase complex. Additional passaging of the intermediate variants and cloning made it possible to obtain pairs of strains that differed by a single amino acid substitution. Comparative analysis of replicative activity, receptor specificity, and virulence of these variants revealed two mechanisms responsible for increased pathogenicity of the virus for mice. Thus, (1) substitutions in HA (Asp225Gly or Gln226Arg) and compensatory mutation decreasing the charge of HA (Lys123Asn, Lys157Asn, Gly158Glu, Asn159Asp, or Lys212Met) altered viral receptor-binding specificity and restored the functional balance between HA and NA; (2) Phe35Leu substitution in the PA protein increased viral polymerase activity.     

Functional consequences of alterations to amino acids located in the catalytic center (isoleucine 348 to threonine 357) and nucleotide-binding domain of the Ca2+-ATPase of sarcoplasmic reticulum

The sequence of 10 amino acids (ICSDKTGTLT357) at the site of phosphorylation of the rabbit fast twitch muscle Ca2+-ATPase is highly conserved in the family of cation-transporting ATPases. We changed each of the residues flanking Asp351, Lys352, and Thr353 to an amino acid differing in size or polarity and assayed the mutant for Ca2+ transport activity and autophosphorylation with ATP or P1. We found that conservative changes (Ile----Leu, Thr----Ser, Gly----Ala) or the alteration of Cys349 to alanine did not destroy Ca2+ transport activity or phosphoenzyme formation, whereas nonconservative changes (Ile----Thr, Leu----Ser) did disrupt function. These results indicate that very conservative changes in the amino acids flanking Asp351, Lys352, and Thr353 can be accommodated. A number of mutations were also introduced into amino acids predicted to be involved in nucleotide binding, in particular those in the conserved sequences KGAPE519, RDAGIRVIMITGDNK629, and KK713. Our results indicate that amino acids KGAPE519, Arg615, Gly618, Arg620, and Lys712-Lys713 are not essential for nucleotide binding, although changes to Lys515 diminished Ca2+ transport activity but not phosphoenzyme formation. Changes of Gly626 and Asp627 abolished phosphoenzyme formation with both ATP and Pi, indicating that these residues may contribute to the conformation of the catalytic center.     

A frameshift mutation results in a truncated alpha 1-antitrypsin that is retained within the rough endoplasmic reticulum

The major physiological role of the serine protease inhibitor alpha 1-antitrypsin (alpha 1-AT) is to protect elastic fibers in the lung from excessive hydrolysis by neutrophil elastase. Genetic deficiency of alpha 1-AT predisposes individuals toward the development of emphysema. We have cloned and characterized a mutant alpha 1-AT gene from an individual exhibiting a total absence of immunoreactive alpha 1-AT in serum. Nucleotide sequence analysis of this "null" allele has demonstrated a TC dinucleotide deletion within the codon for Leu318 in exon IV. This frame-shift mutation results in the generation of a premature termination codon at residue 334, which is upstream of the active inhibitory site. To determine the biochemical basis of the null phenotype, the mutant and normal genes were transferred into mouse hepatoma cells for expression analysis. Pulse-chase experiments demonstrated that the mutant gene is expressed into a truncated protein of 45 kDa, which is retained within the rough endoplasmic reticulum. The complete lack of secretion of the truncated protein is consistent with the absence of immunoreactive alpha 1-AT in the patient's serum. In addition, a G to A transition was identified in exon II of the mutant gene, changing the codon for Arg101 to His101. Finally, an A to C transversion was identified in exon V changing the codon for Glu376 to Asp376. Since the latter conservative amino acid substitution has previously been identified in the common PiM2 variant, the frame-shift mutation might have occurred on a PiM2 background chromosome. Using the birthplace of this index case, this mutant alpha 1-AT allele has been designated "nullHong Kong."     

Disruption of the 290-342 salt bridge is not responsible for the secretory defect of the PiZ alpha 1-antitrypsin variant

Crystallographic studies have previously suggested that Lys290 forms a salt bridge with Glu342 in the serine protease inhibitor alpha 1-antitrypsin. Disruption of the formation of this structural feature by a Glu to Lys substitution at residue 342 in the PiZ variant has been implicated in causing the defective secretion of this mutant protein from hepatocytes (10-15% of normal). To test the validity of this hypothesis, mutant human alpha 1-antitrypsin cDNA constructs coding for specific amino acid substitutions at residues 290 and 342 were generated and the corresponding mutant proteins were expressed in mouse hepatoma cells. When the potential to form the salt bridge was reestablished by a Lys290 to Glu290 substitution in the PiZ variant, its secretion was increased to only 38% of normal. Furthermore, disruption of this structural feature by a Lys290 to Glu290 substitution in the normal inhibitor failed to reduce the secretion of alpha 1-antitrypsin to the extent observed for the PiZ variant (73% of normal). Finally, substitution of the neutral amino acid Gln at residue 342 only reduced the secretion of alpha 1-antitrypsin to 55% of normal. Of all mutant proteins tested, those bearing Lys at position 342 were secreted at the lowest levels. These findings demonstrate that although disruption of the 290-342 salt bridge does affect the secretion of alpha 1-antitrypsin, it is the substitution of Lys at residue 342 that causes the dramatic secretory defect of the PiZ variant.     

Conformational rearrangement of beta-lactoglobulin upon interaction with an anionic membrane

The recent availability of the SHV-1 beta-lactamase crystal structure provides a framework for the understanding of the functional role of amino acid residues in this enzyme. To that end, we have constructed by site-directed mutagenesis 18 variants of the SHV beta-lactamase: an extended spectrum group: Gly238Ser, Gly238Ser-Glu240Lys, Asp104Lys-Gly238Ser, Asp104Lys-Thr235Ser-Gly238Ser, Asp179Asn, Arg164His, and Arg164Ser; an inhibitor resistant group: Arg244Ser, Met69Ile, Met69Leu, and Ser130Gly; mutants that are synergistic with those that confer resistance to oxyimino-cephalosporins: Asp104Glu, Asp104Lys, Glu240Lys, and Glu240Gln; and structurally conserved mutants: Thr235Ser, Thr235Ala and Glu166Ala. Among the extended spectrum group the combination of high-level ampicillin and cephalosporin resistance was demonstrated in the Escherichia coli DH10B strains possessing the Gly238Ser mutation: Gly238Ser, Gly238Ser-Glu240Lys, Asp104Lys-Gly238Ser, and Asp104Lys-Thr235Ser-Gly238Ser. Of the inhibitor resistant group, the Ser130Gly mutant was the most resistant to ampicillin/clavulanate. Using a polyclonal anti-SHV antibody, we assayed steady state protein expression levels of the SHV beta-lactamase variants. Mutants with the Gly238Ser substitution were among the most highly expressed. The Gly238Ser substitution resulted in an improved relative k(cat)/K(m) value for cephaloridine and oxyimino-cephalosporins compared to SHV-1 and Met69Ile. In our comparative survey, the Gly238Ser and extended spectrum beta-lactamase variants containing this substitution exhibited the greatest substrate versatility against penicillins and cephalosporins and greatest protein expression. This defines a unique role of Gly238Ser in broad-spectrum beta-lactam resistance in this family of class A beta-lactamases.     

Two new haemoglobins: haemoglobin Perspolis (alpha 64 (E13) Asp leads to Tyr) and haemoglobin J-Kurosh (alpha 19 (AB) Ala leads to Asp).

Two new haemoglobins are described which were found during a regular survey on voluntary blood donors in Iran. They are haemoglobin Perspolis [alpha 64 (E13) Asp leads to Tyr] and haemoglobin J-Kurosh [alpha 19 (AB) Ala leads to Asp]. The amino acid substitution in these two variants was determined by fingerprinting and amino acid analysis of the tryptic peptides and thermolytic peptides derived from abnormal tryptic peptides. Neither haemoglobin was associated with clinical symptoms.     

Amino acid sequence of piratoxin-II, a myotoxic lys49 phospholipase A(2) homologue from Bothrops pirajai venom

The complete amino acid sequence of the 121 amino acid residues of piratoxin II, a phospholipase A(2) like myotoxin from Bothrops pirajai venom, is reported. PrTX-II is a basic protein with a molecular mass of 13740 Da, a calculated pI of 9.03, but an experimental pI of 8.4 +/- 0.2, showing sequence similarity with other bothropic (90-99%) or non-bothropic ( approximately 80%) Lys49 PLA(2)-like myotoxins. This similarity falls to approximately 70% when this sequence is aligned with that of Asp49 PLA(2). Due to the substitution of Asp49 by Lys49 and alterations in the calcium binding loop structure, as the replacement of Gly32 by Leu32, piratoxin-II shows no PLA(2) activity when assayed on egg yolk. Piratoxin-II showed the same primary structure as piratoxin-I, except that it has Lys116 for Leu116. Despite this slightly higher basicity at the C-terminal region, piratoxin-II was shown to be less myotoxic than piratoxin-I. The change Leu --> Lys induced an alteration of the molecule surface shape and probably of the environment charge high enough to slightly decrease the myotoxic activity. When aligned with B. jararacussu bothropstoxin-I and with B. asper Basp-II, piratoxin-II revealed a single (position 132) and a quintuple (positions 17, 90, 111, 120 and 132) amino acid substitution, respectively, suggesting a common evolutionary origin for these three myotoxins.     

Characterization of the normal alpha 1-antitrypsin allele Vmunich: a variant associated with a unique protein isoelectric focusing pattern.

alpha 1-Antitrypsin (alpha 1AT), the major serum inhibitor of neutrophil elastase, is a highly polymorphic protein associated with isoelectric focusing (IEF) patterns typical for each variant. alpha 1AT Vmunich, a previously unreported normal alpha 1AT variant, has a unique IEF banding pattern in which the 7 and 8 alpha 1AT protein bands focus with the normal M-type 7 and 8 bands, despite the fact that the major fraction of the Vmunich protein focuses in the "V" region of the IEF gel. To characterize the molecular basis of this variant and its unique IEF pattern, DNA sequence analysis of the coding exons of the Vmunich alpha 1AT gene was carried out using the polymerase chain reaction. The Vmunich allele differed from the common normal M1(Val213) alpha 1AT allele by a single nucleotide substitution of cytosine for adenosine, with the resultant amino acid change Asp2 GAT----Ala GCT. Inheritance of the allele was confirmed by family analysis using allele-specific amplification with the polymerase chain reaction. The Asp2----Ala mutation explains the cathodal position of the Vmunich protein on IEF, as there is a substitution of a negatively charged amino acid by a neutral one.(ABSTRACT TRUNCATED AT 250 WORDS)     

Synthetic study on the structure-activity relationship of sperm activating peptides from the jelly coat of sea urchin eggs

Various analogue peptides with substitution and deletion of amino acid residues have been synthesized by liquid phase method for Sperm Activating Peptides from the jelly coat of sea urchin eggs. The deletion of C-terminal Gly reduced the activity to about 1/3000, while removal of N-terminal Gly reduced the activity to 1/10. The residues Ser5 and Asp3 were replaced by Lys without significant loss of activity. Substitution of Phe2 by Gly, Ala or Pro markedly reduced the activity by the factor of 10(4)-10(6), in contrast to Tyr-substitution retaining almost full activity, indicating the essential role of the aromatic residue in exerting the activity. Substitutions, Asp3 to Glu and Gly10 to Pro, increased the activity 5-fold and 500-fold, respectively.     

Amino acid sequence of seminalplasmin, an antimicrobial protein from bull semen

Analytical ultracentrifugation of highly purified seminalplasmin revealed a molecular mass of 6300. Amino acid analysis of the protein preparation indicated the absence of sulfur-containing amino acids cysteine and methionine. The amino acid sequence of seminalplasmin was determined by manual Edman degradation of peptides obtained by proteolytic enzymes trypsin, chymotrypsin and thermolysin: NH₂-Ser Asp Glu Lys Ala Ser Pro Asp Lys His His Arg Phe Ser Leu Ser Arg Tyr Ala Lys Leu Ala Asn Arg Leu Ser Lys Trp Ile Gly Asn Arg Gly Asn Arg Leu Ala Asn Pro Lys Leu Leu Glu Thr Phe Lys Ser Val-COOH. The number of amino acids according to the sequence were 48, the molecular mass 6385. As predicted from the sequence, seminalplasmin very likely contains two α-helical domains in which residues 8-17 and 40-48 are involved. No evidence for the existence of β-sheet structures was obtained. Treatment of seminalplasmin with the above proteases as well as with amino peptidase M and carboxypeptidase Y completely eliminated biological activity.     

The amino acid sequence of human chorionic gonadotropin. The alpha subunit and beta subunit.

The amino acid sequences of both the alpha and beta subunits of human chorionic gonadotropin have been determined. The amino acid sequence of the alpha subunit is: Ala - Asp - Val - Gln - Asp - Cys - Pro - Glu - Cys-10 - Thr - Leu - Gln - Asp - Pro - Phe - Ser - Gln-20 - Pro - Gly - Ala - Pro - Ile - Leu - Gln - Cys - Met - Gly-30 - Cys - Cys - Phe - Ser - Arg - Ala - Tyr - Pro - Thr - Pro-40 - Leu - Arg - Ser - Lys - Lys - Thr - Met - Leu - Val - Gln-50 - Lys - Asn - Val - Thr - Ser - Glu - Ser - Thr - Cys - Cys-60 - Val - Ala - Lys - Ser - Thr - Asn - Arg - Val - Thr - Val-70 - Met - Gly - Gly - Phe - Lys - Val - Glu - Asn - His - Thr-80 - Ala - Cys - His - Cys - Ser - Thr - Cys - Tyr - Tyr - His-90 - Lys - Ser. Oligosaccharide side chains are attached at residues 52 and 78. In the preparations studied approximately 10 and 30% of the chains lack the initial 2 and 3 NH2-terminal residues, respectively. This sequence is almost identical with that of human luteinizing hormone (Sairam, M. R., Papkoff, H., and Li, C. H. (1972) Biochem. Biophys. Res. Commun. 48, 530-537). The amino acid sequence of the beta subunit is: Ser - Lys - Glu - Pro - Leu - Arg - Pro - Arg - Cys - Arg-10 - Pro - Ile - Asn - Ala - Thr - Leu - Ala - Val - Glu - Lys-20 - Glu - Gly - Cys - Pro - Val - Cys - Ile - Thr - Val - Asn-30 - Thr - Thr - Ile - Cys - Ala - Gly - Tyr - Cys - Pro - Thr-40 - Met - Thr - Arg - Val - Leu - Gln - Gly - Val - Leu - Pro-50 - Ala - Leu - Pro - Gin - Val - Val - Cys - Asn - Tyr - Arg-60 - Asp - Val - Arg - Phe - Glu - Ser - Ile - Arg - Leu - Pro-70 - Gly - Cys - Pro - Arg - Gly - Val - Asn - Pro - Val - Val-80 - Ser - Tyr - Ala - Val - Ala - Leu - Ser - Cys - Gln - Cys-90 - Ala - Leu - Cys - Arg - Arg - Ser - Thr - Thr - Asp - Cys-100 - Gly - Gly - Pro - Lys - Asp - His - Pro - Leu - Thr - Cys-110 - Asp - Asp - Pro - Arg - Phe - Gln - Asp - Ser - Ser - Ser - Ser - Lys - Ala - Pro - Pro - Pro - Ser - Leu - Pro - Ser-130 - Pro - Ser - Arg - Leu - Pro - Gly - Pro - Ser - Asp - Thr-140 - Pro - Ile - Leu - Pro - Gln. Oligosaccharide side chains are found at residues 13, 30, 121, 127, 132, and 138. The proteolytic enzyme, thrombin, which appears to cleave a limited number of arginyl bonds, proved helpful in the determination of the beta sequence.     

Identification of Asp218 and Asp326 as the principal Mg2+ binding ligands of the homing endonuclease PI-SceI

The monomeric homing endonuclease PI-SceI harbors two catalytic centers which cooperate in the cleavage of the two strands of its extended recognition sequence. Structural and biochemical data suggest that catalytic center I contains Asp218, Asp229, and Lys403, while catalytic center II contains Asp326, Thr341, and Lys301. The analogy with I-CreI, for which the cocrystal structure with the DNA substrate has been determined, suggests that Asp218 and Asp229 in catalytic center I and Asp326 and Thr341 in catalytic center II serve as ligands for Mg(2+), the essential divalent metal ion cofactor which can be replaced by Mn(2+) in vitro. We have carried out a mutational analysis of these presumptive Mg(2+) ligands. The variants carrying an alanine or asparagine substitution bind DNA, but (with the exception of the D229N variant) are inactive in DNA cleavage in the presence of Mg(2+), demonstrating that these residues are important for cleavage. Our finding that the PI-SceI variants carrying single cysteine substitutions at these positions are inactive in the presence of the oxophilic Mg(2+) but active in the presence of the thiophilic Mn(2+) suggests that the amino acid residues at these positions are involved in cofactor binding. From the fact that in the presence of Mn(2+) the D218C and D326C variants are even more active than the wild-type enzyme, it is concluded that Asp218 and Asp326 are the principal Mg(2+) ligands of PI-SceI. On the basis of these findings and the available structural information, a model for the composition of the two Mg(2+) binding sites of PI-SceI is proposed.     

Essential, completely conserved glycine residue in the domain III S2-S3 linker of voltage-gated calcium channel alpha1 subunits in yeast and mammals

Voltage-gated Ca2+ channels (VGCCs) mediate the influx of Ca2+ that regulates many cellular events, and mutations in VGCC genes cause serious hereditary diseases in mammals. The yeast Saccharomyces cerevisiae has only one gene encoding the putative pore-forming alpha1 subunit of VGCC, CCH1. Here, we identify a cch1 allele producing a completely nonfunctional Cch1 protein with a Gly1265 to Glu substitution present in the domain III S2-S3 cytoplasmic linker. Comparison of amino acid sequences of this linker among 58 VGCC alpha1 subunits from 17 species reveals that a Gly residue whose position corresponds to that of the Cch1 Gly1265 is completely conserved from yeasts to humans. Systematic amino acid substitution analysis using 10 amino acids with different chemical and structural properties indicates that the Gly1265 is essential for Cch1 function because of the smallest residue volume. Replacement of the Gly959 residue of a rat brain Cav1.2 alpha1 subunit (rbCII), positionally corresponding to the yeast Cch1 Gly1265, with Glu, Ser, Lys, or Ala results in the loss of Ba2+ currents, as revealed by the patch clamp method. These results suggest that the Gly residue in the domain III S2-S3 linker is functionally indispensable from yeasts to mammals. Because the Gly residue has never been studied in any VGCC, these findings provide new insights into the structure-function relationships of VGCCs.     

Inheritance of PiM subtypes. A study of 151 families with a total of 242 children and of 142 mother-child pairs.

Pi phenotypes were classified by isoelectric focusing in sera of 151 families with a total of 242 children and in sera of 142 mother-child pairs. The six common subtypes of PiM are genetically determined by three alleles named PiM1, PiM2, and PiM3. No exceptions to the postulated mode of inheritance have been found. The possibility of further heterogeneity of the intermediate variant PiM3 is discussed.     

In vitro stability of growth hormone releasing factor (GRF) analogs in porcine plasma.

The stability of growth-hormone releasing factor (growth regulating factor; GRF) analogs in porcine plasma was examined. GRF analogs were incubated in porcine plasma at 37 degrees C, extracted and subsequently analyzed using high performance liquid chromatography (HPLC). GRF(1-29)-NH2 was rapidly broken down in the plasma with a degradation rate of t1/2 = 13 min. The primary degradation product was identified as GRF(3-29)-NH2. Substitution of Gly15 by Ala15 slightly prolonged the plasma half-life (t1/2 = 17 min) and the major degradative fragment was found to be [Ala15]GRF(3-29)-NH2. The cleavage between the 2 and 3 position of the peptide was not inhibited by trasylol at a concentration of 1,000 KIU/ml but was dramatically reduced by the combined use of diprotin A and trasylol. Absence of the free amino group at the N-terminus and/or substitution of a D-amino acid residue at the penultimate position completely prevented cleavage between the 2 and 3 position in the structural linear GRF analogs. Side-chain to side-chain cyclization between Asp8 and Lys12 amino acid residues significantly improved the stability of GRF in plasma with t1/2 greater than 2 hr. An additional stability was provided by substitution of D-Ala2 for Ala2 in the structural cyclic analog. Cyclization between Lys21 and Asp25 also improved the stability of the GRF peptide in the plasma. Stability was further enhanced by the presence of D-Ala2 or by forming a dicyclic analog through an additional linkage between Asp8 and Lys12.     

Hb J-Singa (alpha-78 Asn leads to Asp), a newly discovered hemoglobin variant with the same amino acid substitution as one of the two present in Hb J-Singapore (alpha-78 Asn leads to, alpha-79 Ala leads to Gly)

A new fast-moving alpha-chain Hb variant with an Asn leads to Asp substitution at position alpha-78 was found in a French-Acadian family living in Eastern Canada. The identical substitution was reported in Hb J-Singapore, which also had an additional Ala leads to Gly substitution at position alpha-79. The new variant, which did not result in any clinical symptoms, was named accordingly, Hb J-Singa.     

Alpha1-antitrypsin: further genetic heterogeneity revealed by isoelectric focusing.

Alpha1-antitrypsin is a major human serum protein that shows an extensive polymorphism. Genetic heterogeneity has previously been demonstrated by starch gel electrophoresis. By applying analytical isoelectric focusing (pH 3.5--5.0) to this system, we found a common variant, Pi M3, with an isoelectric point between those of Pi M1 and Pi M2. The gene frequency of this variant was .11 in U.S. whites and .054 in blacks. When PiM3 and PiM1 are included in the Pi system, the heterozygosity at the Pi locus is five times greater in whites and 10 times greater in blacks than that detected by earlier electrophoretic techniques.