Clostridial Amino acid sequence

As was pointed out previously, clostridial ferredoxins are closely related in spectral properties, iron, and inorganic sulfide content, and amino acid composition. The recent work of Tanaka et al. (100) shows that this similarity applies also to the amino acid sequence of these proteins. Preliminary results indicated that C. butyricum ferredoxin, like C. pasteurianum, contains 55 amino acid residues (3 in addition to those in Table 6), the same glutaminyl-glutamic acid carboxyl-terminal sequence, and the same aminoterminal amino acid, alanine. Their results show also the isomorphic replacement of certain amino acids, such as phenylalanine for tyrosine. 

Whereas the use of synthetic substrates in lieu of native collagen is appropriate in studies with collagenase from clostridial sources, their use in studies of collagenases derived from vertebrate sources cannot be endorsed at this time. The actual amino acid sequence and or other structural requirements that may be recognized by vertebrate collagenases are still unknown. Until these requisites have been determined, we will not know whether splitting of a synthetic substrate represents nonsi)Ccific peptidase activity or specific collagenolytic effect. 

Fig. 2. Structure and active site of clostridial neurotoxins. The upper panel shows the structure of CNTs, and the segments that show significant homology between the different serotypes are in black (Minton, 1995). The highest homology is shown by a short segment corresponding to the amino acid residues 216-244 in TeTx. This segment contains the zinc-binding motif of metallo-proteinases (zincins) and it is dissimilar to the consensus sequence of the metzincin metallo-proteinase family (Jiang and Bond, 1992)...

Figure 4. Amino acids common to sequences of four clostridial ferredoxins...

Figure 4 illustrates those amino acids common to four clostridial ferredoxins that have been sequenced and those residues that are common to all four sequences. The positions of the eight cysteine residues are common to all the proteins. There is no doubt the cysteine acts as a ligand for the iron as well as the sulfide on the basis of much experimental evidence. 

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