Structural and functional characterization of proteolytic fragments derived from the C-terminal regions of bovine fibrinogen.

A number of new as well as previously described fragments derived from the D region of bovine fibrinogen by limited proteolysis have been characterized by sequence analysis, differential scanning calorimetry and circular dichroism. Determination of the extremities of the polypeptide chains forming individual fragments allowed the scheme of proteolysis and the borders between domains in the D region of fibrinogen to be established. It was also found that the most thermostable region of the D fragment (TSD) can be substantially reduced in size without loss of its compact structure. The alpha-helical content of the newly prepared 21-kDa TSD2 and 16-kDa TSD3 fragments were 82% and 75%, respectively, strongly supporting a coiled-coil structure for this region of the fibrinogen molecule. The DX and DZ fragments, prepared from a chymotryptic digest of the DLA fragment, were found to be similar to the DL and DY fragments, respectively, except for an internal cleavage at K393-T394 in their beta chains. This cleavage leads to destabilization of all thermolabile domains, indicating interaction between them. The DL and DY fragments, containing only one polymerization site in their beta chains, were able to inhibit fibrin polymerization at high concentration. However, these same fragments failed to bind to fibrin-Sepharose under conditions where their structural analogues, DX and DZ, were tightly bound, indicating that cleavage after K393 substantially increases the affinity of this site.

A proposal for a coherent mammalian histone H1 nomenclature correlated with amino acid sequences.

Bio-Rex 70 chromatography was combined with reverse-phase (RP) HPLC to fractionate histone H1 zero and 4 histone H1 subtypes from human placental nuclei as previously described (Parseghian MH et al., 1993, Chromosome Res 1:127-139). After proteolytic digestion of the subtypes with Staphylococcus aureus V8 protease, peptides were fractionated by RP-HPLC and partially sequenced by Edman degradation in order to correlate them with human spleen subtypes (Ohe Y, Hayashi H, Iwai K, 1986, J Biochem (Tokyo) 100:359-368; 1989, J Biochem (Tokyo) 106:844-857). Based on comparisons with the sequence data available from other mammalian species, subtypes were grouped. These groupings were used to construct a coherent nomenclature for mammalian somatic H1s. Homologous subtypes possess characteristic patterns of growth-related and cAMP-dependent phosphorylation sites. The groupings defined by amino acid sequence also were used to correlate the elution profiles and electrophoretic mobilities of subtypes derived from different species. Previous attempts at establishing an H1 nomenclature by chromatographic or electrophoretic fractionations has resulted in several misidentifications. We present here, for the first time, a nomenclature for somatic H1s based on amino acid sequences that are analogous to those for H1 zero and H1t. The groupings defined should be useful in correlating the many observations regarding H1 subtypes in the literature.

Covalent structure of botulinum neurotoxin type A: location of sulfhydryl groups, and disulfide bridges and identification of C-termini of light and heavy chains.

Botulinum neurotoxin Type A is synthesized by Clostridium botulinum as a approximately 150 kD single chain polypeptide. The posttranslational processing of the 1296 amino acid residue long gene product involves removal of the initiating methionine, formation of disulfide bridges, and limited proteolysis (nicking) by the bacterial protease(s). The mature dichain neurotoxin is made of a approximately 50-kD light chain and a approximately 100-kD heavy chain connected by a disulfide bridge. DNA derived amino acid sequence predicted a total of 9 Cys residues (Binz et al., 1990, J. Biol. Chem. 265, 9153-9158; Thompson et al., 1990, Eur. J. Biochem. 189, 73-81). Treatment of the dichain neurotoxin, dissolved in 6 M guanidine. HCl, with 4-vinylpyridine converted 5 Cys residues into S-pyridylethyl cysteine residues; but alkylation after mercaptolysis converted all 9 Cys residues in the S-pyridylethylated form. After confirming the predicted number of Cys residues by amino acid analysis, the positions of the 5 Cys residues carrying sulfhydryl groups and the 4 involved in disulfide bridges were determined by comparing the elution patterns in reversed-phase HPLC of the cyanogen bromide mixtures of the exclusively alkylated and the mercaptolyzed-alkylated neurotoxin. The chromatographically isolated components were identified by N-terminal amino acid sequence analysis. The HPLC patterns showed characteristic differences. The Cys residues predicted in positions 133, 164, 790, 966, and 1059 were found in the sulfhydryl form; Cys 429 and 453 were found disulfide-bridge connecting the light and heavy chains, and Cys 1234 and 1279 were found in an intrachain disulfide-bridge near the C-terminus in the heavy chain.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for two distinct major protein components, PAR 1 and PAR 2, in the paraflagellar rod of Trypanosoma cruzi. Complete nucleotide sequence of PAR.

The previously identified major protein components of the paraflagellar rod in Trypanosoma cruzi, PAR 1 and PAR 2, were analyzed to determine if they are distinct proteins or different conformations of a single polypeptide as has been suggested for other trypanosomatids. Amino acid sequence analysis showed PAR 1 and PAR 2 to be two distinct polypeptides. Antibodies specific against either PAR 1 or PAR 2 were shown to each react with a distinct band in Western blots of paraflagellar isolates of T. cruzi and other trypanosomatids if rigorous protease inhibition was used. The PAR 2 message was isolated and characterized by Northern blot and nucleic acid sequence analysis. Preliminary analysis of the PAR 2 gene indicates that PAR 2 is a member of a multigene family with all members residing on a single chromosome.

Limited proteolysis of tetanus toxin. Relation to activity and identification of cleavage sites.

Tetanus toxin is synthesized by Clostridium tetani as a 151-kDa peptide chain. The primary gene product is processed post-translationally by removal of the initiating methionine residue, formation of disulfide bridges and limited proteolysis by bacterial or exogenous proteinases. The mature toxins consist of a 52-kDa light chain and a 98-kDa heavy chain, linked together by a disulfide bond. Proteolytic nicking is accompanied by increased pharmacological potency. To identify the structural alterations involved, single-chain toxin has been subjected to limited proteolysis with various enzymes. The new N-termini have been determined by Edman degradation and the C-termini by isolation of short C-terminal peptide fragments and subsequent analysis of the sequence and composition. All two-chain toxins result from proteolytic nicking within the 17-residue segment of residues 445-461. Thus, the protease(s) of the culture broth cleave on the C-terminal side of Glu449 and partially Ala456, giving rise to two heavy chain N-termini. Trypsin and clostripain first attack the C-terminal of Arg454 and later Arg448, whereas endoproteinase Arg-C cleaves the former bond only. Chymotrypsin and endoproteinase Glu-C each split a single peptide bond, i.e. that located after Tyr452 and Glu449, respectively. Papain gives rise to a large number of cleavages within the 17-residue segment, the new C-terminus being Thr445 or Asn446 and the new N-terminus being Asp460 or Leu461. Further papain digestion leads to an additional cleavage within the heavy chain between Ser863 and Lys864. The original N-terminal Pro1 and C-terminal Asp1314, predicted from the nucleotide sequence, are conserved in all proteolytic digests. The pharmacological activity of the various two-chain toxins was 5-11 times that of the single-chain toxin, as estimated from the inhibition of [3H]noradrenaline release from rat-brain homogenate. The present data on the processing and activation by limited proteolysis prove the existence of several active tetanus isotoxins. These data, together with our previous data on the localization of disulfide bridges and sulfhydryl groups (Krieglstein, K., Henschen, A., Weller, U. & Habermann, E. (1990) Eur. J. Biochem. 188, 39-45), provide the detailed protein chemical characterization of the tetanus isotoxins.