The multi-domain, cell-envelope proteinases encoded by the genes prtB of La
ctobacillus delbrueckii subsp. bulgaricus, prtH of Lactobacillus helveticus
, prtP of Lactococcus lactis, scpA of Streptococcus pyogenes and csp of Str
eptococcus agalactiae have been compared using multiple sequence alignment,
secondary structure prediction and database homology searching methods. Th
is comparative analysis has led to the prediction of a number of different
domains in these cell-envelope proteinases, and their homology, characteris
tics and putative function are described. These domains include, starting f
rom the N-terminus, a pre-pro-domain for secretion and activation, a serine
protease domain (with a smaller inserted domain), two large middle domains
A and B of unknown but possibly regulatory function, a helical spacer doma
in, a hydrophilic cell-wall spacer or attachment domain, and a cell-wall an
chor domain. Not all domains are present in each cell-envelope proteinase,
suggesting that these multi-domain proteins are the result of gene shufflin
g and domain swapping during evolution.