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A protein is usually classified into one of the following four structural classes: all α, all β, (a + B) and α/β. In this paper, based on the maximum correlation-coefficient principle, a new formulation is proposed for predicting the structural class of a protein according to its amino acid composition. Calculations have been made for a development set of proteins from which the amino acid compositions for the standard structural classes were derived, and an independent set of proteins which are outside the development set. The former can test the self consistency of a method and the latter can test its extrapolating effectiveness. In both cases, the results showed that the new method gave a considerably higher rate of correct prediction than any of the previous methods, implying that a significant improvement has been achieved by implementing the maximum-correlation-coefficient principle in the new method. [ABSTRACT FROM AUTHOR]

Monoamine oxidases (MAO) A and B show a high degree of amino acid similarity. Apart from the NH2-terminus, which contains an ADP-binding consensus sequence, little is known about their structural features or the sequences involved in the binding of substrates. In the present paper, we have studied the structure/function relationships of MAOs by constructing 18 different chimeric forms of MAO, engineered by moving progressively the junction between the NH2-terminus of one MAO form with the COOH-terminus of its isoenzyme. After transient expression in HEK-293 cells, the properties of these chimeric enzymes were investigated using both selective and nonselective substrates and inhibitors. Whereas exchange of the ADP-binding sequence did not modify the catalytic properties of either MAO isoforms, chimeras with increasing length of the NH2-terminus of MAO-A (up to residue 256) showed a marked decrease in affinity towards the MAO-B substrate phenylethylamine and the inhibitor N-(2-aminoethyl)-5-chloro-2-pyridine carboxamide · HCI (lazabemide) when compared to wild-type MAO-B. No major changes were observed in the kcat, values of these chimeras. From the data obtained, two sequences, i.e. 62–103 and 146–220, appeared of particular importance in constituting the binding site of MAO-B. On the other hand, the catalytic properties and specificity of MAO-A appeared to be relatively insensitive to substitution of both the NH2-- (up to position 112) and COOH-termini (from residue 395) of MAO-A with the corresponding MAO-B sequences. However, further modification of the central 283-residue sequence of MAO-A did not appear compatible with enzymic activity. None of the engineered chimeras showed a shift in specificity from one isoform to the other. [ABSTRACT FROM AUTHOR]

Information on the regulation and structure–function relation of enzymes involved in DNA precursor synthesis is pivotal, as defects in several of these enzymes have been found to cause depletion or deletion of mitochondrial DNA resulting in severe diseases. Here, the effect of amino acid 106 on the enzymatic properties of the cell-cycle-regulated human cytosolic thymidine kinase 1 (TK1) is investigated. On the basis of the previously observed profound differences between recombinant TK1 with Val106 (V106WT) and Met106 (V106M) in catalytic activity and oligomerization pattern, we designed and characterized nine mutants of amino acid 106 differing in size, conformation and polarity. According to their oligomerization pattern and thymidine kinetics, the TK1 mutants can be divided into two groups. Group I (V106A, V106I and V106T) behaves like V106WT, in that pre-assay exposure to ATP induces reversible transition from a dimer with low catalytic activity to a tetramer with high catalytic activity. Group II (V106G, V106H, V106K, V106L and V106Q) behaves like V106M in that they are permanently high activity tetramers, irrespective of ATP exposure. We conclude that size and conformation of amino acid 106 are more important than polarity for the catalytic activity and oligomerization of TK1. The role of amino acid 106 and the sequence surrounding it for dimer–tetramer transition was confirmed by cloning the putative interface fragment of human TK1 and investigating its oligomerization pattern. [ABSTRACT FROM AUTHOR]

The complete amino acid sequence (72 amino acid residues) of a double-headed proteinase inhibitor from seeds of Vicia angustifolia L. var. segetalis Koch has been determined and compared with those of other double-headed inhibitors of known structure. Sequencing was performed by conventional methods with the aid of the fragments produced by reduction and S-carboxymethylation of the enzymatically modified inhibitors, and also using tryptic and chymotryptic peptides. The positions of the 14 half-cystine residues agreed among all the reported primary structures of the legume double-headed inhibitors. However, V. angustifolia inhibitor possessed extensive amino acid differences compared to the others. The phylogenetic relationship among these inhibitors was established using the unweighted pair-group method and revealed that the V. angustifolia inhibitor and the peanut inhibitor B-III had diverged at a relatively earlier stage compared to the other inhibitors. [ABSTRACT FROM AUTHOR]

The amino acid sequence of a single polypeptide chain, B-4, from fowl feather barbs has been determined. The B-4 chain was found to consist of 96 amino acid residues and to have a molecular weight of 10206 in the S-carboxymethylated form. The N terminus of this protein was an N-acetylserine residue. The B-4 protein contained seven S-carboxymethyleysteine residues, six of which arc located in the N-terminal region (residues 1 -26), and other one in C terminus. The central region of the peptide chain was rich in hydrophobic residues. There were homologous amino acids at 66 positions in the sequences of the feather keratins of fowl, emu and silver gull. The variation (substitution, deletion and insertion) in sequence was found to be localized in both terminal sections of the polypeptide chain. The 13-4 protein structure was predicted to contain β-sheet (about 30 %), turn and random-coil-like structure, and no α-helix. β-Sheet structure is mostly located in the central region (residues 22- 70). On the other hands both terminal regions are almost devoid of secondary structure. [ABSTRACT FROM AUTHOR]

The phosphatidylcholine exchange protein from bovine liver consists of a single polypeptide chain and has a blocked N terminus. The protein contains an estimated 244 amino acid residues in accordance with a determined molecular weight of 28 000. The protease from mouse submaxillaris gland cleaved the citraconylated and S-carboxymethylated derivative of the exchange protein at one specific site (Arg14-Glu15) close to the N terminus. Analysis of the two resulting peptides showed that N-acetyl-methionine was the N-terminal residue and gave the sequence of the first 41 residues. The modified protein was also fragmented with the protease from Staphylococcus aureus. The peptides isolated represented 88% of the protein; their sequences were determined by manual and automated Edman degradation. Alignment of a number of these peptides gave the complete sequence of the N-terminal half up to position 122. [ABSTRACT FROM AUTHOR]

The amino acid sequence of a brain-specific protein, S-100, has been determined by the analysis of four cyanogen bromide peptides and fourteen tryptic peptides derived from the protein. The protein chain consists of 91 amino acid residues and has a molecular weight of 10 507. The sequence shows regions of strong clustering of hydrophobic, basic and acidic amino acids, with an apparent calcium-binding site in the acidic cluster. [ABSTRACT FROM AUTHOR]

We have analyzed the amino acid distribution in seven nuclearly encoded and five mitochondrially encoded inner membrane proteins with experimentally well characterized topologies. The mitochondrially encoded proteins conform to the ‘positive inside’ rule, i.e. they have many more positively charged residues in their non-translocated as compared to translocated domains. However, most of the nuclearly encoded proteins do not show such a bias but instead have a surprisingly skewed distribution of Glu residues with an almost ten times higher frequency in the intermembrane space than in the matrix domains. These findings suggest that some, but possibly not all, nuclearly encoded inner membrane proteins may insert into the membrane by a mechanism that does not depend on the distribution of positively charged amino acids. [ABSTRACT FROM AUTHOR]

Rat-liver biliverdin reductase exists in two molecular forms. The major form I has a molecular mass of 34 kDa, while the minor form 2 has a molecular mass of 56 kDa. Form I was converted into a second major form (form 3) with a molecular mass of 68 kDa by a NAD +-dependent peroxisomal dehydrogenase which was induced under conditions of oxidative stress [Frydman, R. B., Tomaro, M. L., Awruch, J. & Frydman, B. (1984) Biochem. Biophys. Res. Commun. 121, 249]. Molecular form 1 from rat kidney was not affected by the dehydrogenase, and a structural explanation for this difference was therefore saught. Both form 1 biliverdin reductases, isolated from rat liver and kidney, were purified to homogeneity using affinity chromatography, FPLC and HPLC techniques. The homogeneous enzymes were found to be identical when compared by their HPLC retention times, amino acid compositions and electrophoretic behaviour on polyacrylamide gels under non-denaturing conditions and on SDg/polyacrylamide gels. On HPLC analysis the peptides resulting from the CNBr cleavage were found to be the same for both enzymes, when either the native enzymes or their thioethylpyridine derivatives were compared. When the HPLC fingerprints of the tryptic digests were compared, they were found to be very similar, except for a peptide eluting at 31.60 min in the liver digest and at 23.60 min in the kidney digest. When the enzyme from both origins was alkylated with 4-dimethylaminoazobenzene-4'-iodoacetamide and then digested with trypsin, the HPLC fingerprints of the alkylated cysteine-carrying peptides were almost identical, except for a peptide with a retention time of 19.03 min in the liver digest and of 18.19 min in the kidney digest. The liver reductase was not amenable to Edman degradation suggesting a block at the NH2-terminus; in the kidney enzyme, however, it was free and an NH2-terminal sequence of 12 amino acids could be determined. The liver enzyme was found to be more sensitive toward p-hydroxymercuriphenyl sulfonate than the kidney enzyme. [ABSTRACT FROM AUTHOR]

Two of the four electrophoretic histone H2B variants present in wheat embryos have been isolated. The complete primary structure of the H2B(2) variant has been deduced from sets of overlapping peptides generated by CNBr cleavage, Staphyloccocus aureus V8 protease, endoproteinase Arg-C, the post-proline cleaving enzyme, chymotrypsin and cleavage in dilute acid. A minimum of 17 peptides were required to establish the sequence. This variant has a blocked N terminus and comprises a total of 149 amino acids. The C-terminal two-thirds of the protein are highly homologous to vertebrate H2B. In contrast, the N-terminal third is entirely different and contains an N-terminal extension of 23 residues in which the sequence Ala-Glu-Lys or variants are repeated several times. This region is also highly homologous to the H2B from Tetrahymena pyriformis. It shows in addition similarities to wheat H2A(1) and bovine H1. [ABSTRACT FROM AUTHOR]