C. Chan et al., THE COMPLETE AMINO-ACID-SEQUENCE CONFIRMS THE PRESENCE OF PSEUDOAZURIN IN THIOSPHAERA-PANTOTROPHA, Biochemical journal, 308, 1995, pp. 585-590
The complete amino acid sequence, obtained by direct protein sequencin
g, of the pseudoazurin from Thiosphaera pantotropha is reported. It sh
ows sequence identities varying from 46 to 66% with previously sequenc
ed pseudoazurins. Previously identified conserved residues with key fu
nctions in pseudoazurins are found in the protein from T. pantotropha
with the exception of glycine-39, the carbonyl group of which has been
considered as a ligand to the copper, which is replaced by a serine r
esidue. Electrospray-ionization MS (ESI-MS) has shown that pseudoazuri
n from T. pantotropha often contains two polypeptide species differing
in molecular mass by 16 Da, presumably owing to oxidation of a methio
nine residue to a sulphoxide derivative. These two species have differ
ent endoproteinase Arg-C digestion patterns. Conditions for ESI-MS wer
e identified that permitted either the retention or the loss of the si
ngle copper ion associated with the pseudoazurin. The aberrant tendenc
y of T. pantotropha pseudoazurin to form a disulphide-bridged dimer on
SDS/PAGE under some conditions is described.