The amino acid sequence of Neurospora NADP-specific glutamate dehydrogenase. The tryptic peptides

Importance of lysine-286 at the NADP site of glutamate dehydrogenase from Salmonella typhimurium

Affinity labeling studies of NADP(+)-glutamate dehydrogenase from Salmonella typhimurium have shown that the peptide Leu-282-Lys-286 is located near the coenzyme site [Haeffner-Gormley et al. (1991) J. Biol. Chem. 266, 5388-5394]. The present study was undertaken to evaluate the role of lysine-286. The mutant enzymes K286R, K286Q, and K286E were prepared by site-directed mutagenesis, expressed in Escherichia coli, and purified. The Vmax values (micromoles of NADPH per minute per milligram of protein) were similar for WT (270), K286R (529), K296Q (409), and K286E (382) enzymes. As measured at pH 7.9, the Km value for NADPH was much greater for K286E (280 microM) than for WT (9.8 microM), K286R (30 microM), or K286Q (66 microM) enzymes. The efficiencies (kcat/Km) of the WT and K286R mutant were similar (1.2 x 10(3) min-1 microM-1 and 1.0 x 10(3) min-1 microM-1, respectively) while those of K286Q (0.30 x 10(3) min-1 microM-1) and K286E (0.07 x 10(3) min-1 microM-1) were greatly reduced. The decreased efficiency of the K286E mutant results from the increase in Km-NADPH, consistent with a role for a basic residue at position 286 which enhances the binding of NADPH. Plots of Vmax vs pH showed the pH optima to be 8.1-8.3 for all enzymes at saturating NADPH concentrations. A 40-fold increase in Km-NADPH for K286E was observed as the pH increased from 5.98 to 8.08, from which a unique pKe of 6.5 was calculated.(ABSTRACT TRUNCATED AT 250 WORDS)

A ten-residue fragment of an antibody (mini-antibody) directed against lysozyme as ligand in immunoaffinity chromatography

The interaction between an antibody molecule and a protein antigen is an example of "natural" protein modelling. Amino acids of the antigen-binding site consisting of three hypervariable segments (L1, L2, L3) of the light (L) and three (H1, H2, H3) of the heavy (H) chain of an antibody molecule interact with amino acids present in an epitope of a protein. A ten-residue peptide was synthesized with an amino acid sequence analogous to the hypervariable L3 segment of a monoclonal antibody directed against lysozyme. The peptide was immobilized on CH-Sepharose 4B and the affinity adsorbent was used to purify lysozyme added to a detergent extract of insect cells infected with a recombinant baculovirus. This methodology may also be applicable to other antigen-antibody combinations, in immunoaffinity chromatography for selective purification of a protein or in an immunosensor for detection of a protein.

Reactivity of human sera with overlapping synthetic peptides of herpes simplex virus type 1 glycoprotein D

Thirty eight human sera, seropositive for herpes simplex virus (HSV) and 56 human sera, seronegative for HSV by immunofluorescence and by ELISA, were investigated for reactivity with a series of overlapping synthetic peptides of HSV type 1 glycoprotein D (gD-1). Thirty four out of the 38 human sera positive for HSV reacted with peptides located between residues 300 and 369; the HSV-negative sera reacted with six of the gD-1 peptides, but with none of the peptides within residues 300 to 369.

Assay of cytotoxicity and mutagenicity of alkylating agents by using Neurospora spheroplasts

A system relying on the use of Neurospora crassa spheroplasts has been developed for the assay of cytotoxicity and mutagenicity of chemical compounds. Mutagenicity was assayed by using reversion of alleles in the am gene selected to recognize certain specified transitions and also undefined point mutations. Cytotoxicity was quantified by measuring a 'cytotoxicity parameter', m, which appears in the exponential function that fits the survival/dose curve for each compound (under standard incubation conditions). Of the compounds tested, nitrogen mustard (Cl(CH2)2 NMe(CH2)2Cl) was cytotoxic and non-mutagenic, and ethyl nitrosourea was highly mutagenic but not cytotoxic. Of the remaining compounds tested, methyl nitrosourea, butadiene diepoxide, and cis platin (cis diammonia platinum II chloride) all showed comparable mutagenicity per survivor, although the values of m covered a wide range. Differences were found between the different compounds in the effects of the uvs-2 allele on survival and on the preponderance of G to A transitions.

The complete amino-acid sequence of the low-spin class II cytochrome c-556 from Agrobacterium tumefaciens strain B2a

The amino acid sequence of the soluble monohaem cytochrome c-556 from Agrobacterium tumefaciens, strain B2a, has been determined. The sequence was derived from peptides obtained by digestion of the apoprotein with trypsin and chymotrypsin, and by subdigestion of some of the peptides with Staphylococcus aureus protease and thermolysin. Sequencing of the various peptides was achieved by a combination of manual dansyl-Edman degradation and automatic liquid-phase sequence analysis. The main characteristic of this cytochrome is that the haem-binding sequence Cys-Xaa-Yaa-Cys-His occurs in the C-terminal region of the polypeptide chain, the first cysteine being located 11 residues ahead of the C-terminal lysine-122. As such, the protein belongs to cytochrome c sequence class II (sensu Ambler). The cytochrome c-556 is the first example known of a class II cytochrome of the low-spin type isolated from an obligate aerobic organism.

Glycopeptides from variant surface glycoproteins of Trypanosoma Brucei. C-terminal location of antigenically cross-reacting carbohydrate moieties

Glycopeptides have been purified after trypsin or pronase cleavage of variant surface glycoproteins from five antigenic variants of one clone of Trypanosoma brucei. Each peptide has been characterised by its amino acid and sugar composition and partial or complete amino acid sequence. The peptides were assayed in an indirect precipitation radioimmunoassay for inhibition of precipitation of one variant surface glycoprotein by a heterologous antiserum raised against another variant. Two classes of glycopeptide were obtained, those which showed complete inhibition and those which had no inhibitory activity. The non-cross-reacting glycopeptides were all derived from internal sites in the polypeptide chain and had only mannose and glucosamine as the constituents of the glycosyl group with one exception which also contained galactose. The carbohydrate moieties involved in the immunological cross-reaction were found to be attached at or very close to the C-terminus of the protein and contained galactose, mannose and glucosamine. Considerable variation in the size and composition of these glycosyl moieties occurred between the variant glycoproteins and, in two cases, within individual glycoproteins. The immunological cross-reactivity was constant despite this oligosaccharide heterogeneity. There was significant amino acid sequence homology between glycopeptides from certain variants in contrast to the absence of homology observed previously for the N-terminal sequence of intact surface glycoproteins. Some C-terminal glycopeptide sequences suggest the occurrence of proteolytic processing subsequent to glycosylation and prior to variant surface glycoprotein isolation. The terminal amino acid (Asx or Ser) of all isolated variant surface glycoproteins was glycosylated.

New mutational variants of Neurospora NADP-specific glutamate dehydrogenase

The am locus of Neurospora codes for NADP-dependent glutamate dehydrogenase (GDH). Four new am mutants that produced mutationally altered GDH have been characterized. Mutant am119 is a CRM-negative, complementing mutant that maps between am2 and am1. The other three mutants are CRM formers that produce varieties of GDH that can be activated by glutamate or succinate. The GDH of am130 and am131 is similar in terms of activation properties to that of am3. The GDH of am122 requires very high concentrations of dicarboxylate for activity. The mutation in am130 maps between am14 and am2 and resulted in a replacement at residue 75 of the GDH (pro leads to ser). The mutation in am122 maps near am11 and apparently resulted in the replacement of the tryptophan residue at position 389 with an unknown amino acid. The mutation in am131 maps between am2 and am1.

The amino acid sequence of mouse pancreatic ribonuclease. Extremely rapid evolutionary rates of the myomorph rodent ribonucleases

The complete amino acid sequence of mouse pancreatic ribonuclease has been determined by analysis of tryptic, chymotryptic, thermolytic and CNBr peptides and by automatic sequence analysis of the intact protein. The sequence of mouse RNase differs in 20--30% of the positions from other RNase sequences. Three unique or neraly unique substitutions were found, viz. Gly-68 leads to Arg-68, Arg-85 leads to His-85 and Ser-123 leads to Thr-123. All these three residues might be involved in interactions with substrate molecules. A most parsimonious tree of the myomorph rodent RNase shows that after the divergence of rat and mouse, the ribonuclease of rat accumulated substitutions at a rate 2.5--4.3 times as high as the rates in other branches of the tree and 23 times as high as the average rate in the Bovidae ribonuclease evolution. These extreme fluctuations in substitution rate are difficult to reconcile with the hypothesis of the evolutionary clock. The high evolution rate of rat ribonuclease is thought to be caused by positive selection, leading to new functional properties of the enzyme.

Extraction and fingerprint analysis of simian virus 40 large and small T-antigens

A study of simian virus 40 (SV40) T-antigens isolated from productively infected CV1 cells using a variety of different extraction procedures showed that under some conditions the highest molecular weight form of T-Ag (large-T) isolated comigrated on sodium dodecyl sulfate-polyacrylamide gel electrophoresis with large-T from SV40-transformed H65-90B cells. Other faster-migrating forms of large-T are probably generated during the extraction procedure by a protease which is active at low pH, and such forms are probably experimental artifacts. After extraction under conditions which minimize proteolytic degradation of large-T, a further form of T-antigen was isolated; this has an apparent molecular weight in the range 15,000 to 20,000 and is referred to as small-t. Fingerprint analysis of [35S]methionine-labeled SV40 proteins showed that small-t has 10 to 12 methionine peptides whereas large-T has 15 to 18 methionine peptides. All but two of the methionine tryptic peptides present in small-t are also present in large-T. The fingerprint data also showed that T-antigens have no peptides in common with SV40 VP1. Experiments using reagents which inhibit posttranslational cleavage of encephalomyocarditis virus polyproteins showed that these reagents do not affect the synthesis of small-t and suggest that it is not made by proteolytic cleavage of large-T in vivo. An alternative model, which proposes that large-T and small-t are synthesized independently, is discussed in terms of the fingerprint data and the number of methionine tryptic peptides predicted from the primary sequence of SV40 DNA.

Rat alpha-crystallin A chain with an insertion of 22 residues

Rat lens alpha-crystallin contains, besides the usual alphaA and alphaB subunits, an additional minor chain. This subunit was purified by ion-exchange chromatography and its primary structure studied. It appeared to be an elongated alphaA-like chain, having an insertion of 22 residues between position 63 and 64 of an otherwise normal alphaA2 chain. Therefore this subunit was called alphaAIns, i.e. an alphaA chain with an inserted sequence. This inserted region, which contains three methionyl, five basic and no acidic residues, apparently results in an adequately functioning alphaAIns chain. The alphaAIns chain may be the product of a gene which has originated, after duplication of the alphaA gene, by insertion in one of the copies of a stretch of 66 nucleotides of unknown origin, or alternatively be the result of unusual transcription or processing of precursor mRNA (pre-mRNA), leaving an extra 66 nucleotides internally in the mRNA to be translated.

Amino acid replacements resulting from suppression and missense reversion of a chain-terminator mutation in Neurospora

The Neurospora crassa super-suppressor mutation, ssu-1, suppresses the auxotrophic phenotype of the mutant am(17) by inserting tyrosine at residue 313 of NADP-specific glutamate dehydrogenase, a position occupied in the wild type by glutamate. Two classes of am(17) revertants due to further mutation within the am gene have, respectively, tyrosine and leucine at residue 313. These replacements are consistent with a chain-terminating codon in am(17) of either the amber (UAG) or the ochre type (UAA), but are inconsistent with UGA. The Leu313 and Tyr313 variants of the enzyme have effective activity but are grossly different from the wild type in Michaelis constants (especially for ammonium) and heat stabilities at two different pH values. They show smaller but significant differences in these respects from each other.

The amino-acid sequence of the alpha-crystallin A chains of red kangaroo and Virginia opossum

The amino acid sequence of the A chain of the eye lens protein alpha-crystallin from the red kangaroo (Macropus rufus) was completely determined by manual Edman degradation of tryptic, thermolytic and cyanogen bromide peptides. The sequence of the alpha-crystallin A chain from the Virginia opossum (Didelphis marsupialis) was deduced from amino acid analyses and partial Edman degradation of peptides. The 173-residue A chains of kangaroo and opossum differ in six positions, whereas comparison with the bovine alpha-crystallin A chain reveals 17 and 22 substitutions, respectively. Most substitutions occur in the COOH-terminal part of the chain.

The amino acid sequence of Neurospora NADP-specific glutamate dehydrogenase. Peptic and chymotryptic peptides and the complete sequence

Peptic and chymotryptic peptides were isolated form the NADP-specific glutamate dehydrogenase of Neurospora crassa and substantially sequenced. Out of 452 residues in the polypeptide chain, 265 were recovered in the peptic and 427 in the chymotryptic peptides. Together with the tryptic peptides [Wootton, J. C., Taylor, J. G., Jackson, A. A., Chambers, G. K. & Fincham, J. R. S. (1975) Biochem. J. 149, 749-755], these establish the complete sequence of the chain, including the acid and amide assignments, except for seven places where overlaps are inadequate. These remaining alignments are deduced from information on the CNBr fragments obtained in another laboratory [Blumenthal, K. M., Moon, K. & Smith, E. L. (1975), J. Biol. Chem. 250, 3644-3654]. Further information has been deposited as Supplementary Publication SUP 50054 (17 pages) with the British Library (Lending Division), Boston Spa, Wetherby, W. Yorkshire LS23 7BQ, U.K., from whom copies may be obtained under the terms given in Biochem. J. (1975) 145, 5.

The amino acid sequence of Neurospora NADP-specific glutamate dehydrogenase. Peptides from digestion with a staphylococcal proteinase

The extracellular proteinase of Staphylococcus aureus strain V8 was used to digest the NADP-specific glutamate dehydrogenase of Neurospora crassa. Of 35 non-overlapping peptides expected from the glutamate content of the polypeptide chain, 29 were isolated and substantially sequenced. The sequences obtained were valuable in providing overlaps for the alignment of about two-thirds of the sequences found in tryptic peptides [Wootton, J. C., Taylor, J, G., Jackson, A. A., Chambers, G. K. & Fincham, J. R. S. (1975) Biochem. J. 149, 739-748]. The blocked N-terminal peptide of the protein was isolated. This peptide was sequenced by mass spectrometry, and found to have N-terminal N-acetylserine by Howard R. Morris and Anne Dell, whose results are presented as an Appendix to the main paper. The staphylococcal proteinase showed very high specificity for glutamyl bonds in the NH4HCO3 buffer used. Partial splits of two aspartyl bonds, both Asp-Ile, were probably attributable to the proteinase. No cleavage of glutaminyl or S-carboxymethylcysteinyl bonds was found. Additional experimental detail has been deposited as Supplementary Publication SUP 50053 (5 pages) with the British Library (Lending Division), Boston Spa, Wetherby, W. Yorkshire LS23 7BQ, U.K, from whom copies may be obtained under the terms given in Biochem. J. (1975) 1458 5.