{PDOC00293}
{PS00330; HEMOLYSIN_CALCIUM}
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* Hemolysin-type calcium-binding region signature *
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Gram-negative bacteria  produce  a  number of proteins which are secreted into
the growth medium by a mechanism that  does  not  require a cleaved N-terminal
signal sequence. These proteins, while having different functions, seem [1] to
share two properties: they bind calcium  and they contain a variable number of
tandem repeats consisting of a nine amino acid motif rich in glycine, aspartic
acid and asparagine. It has been shown [2] that such  a  domain is involved in
the binding of calcium ions in a parallel beta roll structure.    The proteins
which are currently known to belong to this category are:

 - Hemolysins from  various  species  of bacteria.   Bacterial  hemolysins are
   exotoxins that attack blood  cell  membranes  and cause  cell rupture.  The
   hemolysins which are known to contain such a domain are those from: E. coli
   (gene hlyA),   A. pleuropneumoniae  (gene appA),   A. actinomycetemcomitans
   and P. haemolytica (leukotoxin) (gene lktA).
 - Cyclolysin from Bordetella pertussis (gene cyaA). A multifunctional protein
   which is both an adenylate cyclase and a hemolysin.
 - Extracellular zinc proteases: serralysin (EC 3.4.24.40) from Serratia, prtB
   and prtC from Erwinia chrysanthemi and aprA from Pseudomonas aeruginosa.
 - Nodulation protein nodO from Rhizobium leguminosarum.

We derived a signature pattern from conserved positions in the sequence of the
calcium-binding domain.

-Consensus pattern: D-x-[LI]-x(4)-G-x-D-x-[LI]-x-G-G-x(3)-D
-Sequences known to belong to this class detected by the pattern: ALL.
-Other sequence(s) detected in Swiss-Prot: NONE.

-Note: This pattern  is found once in nodO and the extracellular proteases but
 up to 5 times in some hemolysin/cyclolysins.

-Last update: October 1993 / Text revised.

[ 1] Economou A., Hamilton W.D.O., Johnston A.W., Downie J.A.
     "The Rhizobium nodulation gene nodO encodes a Ca2(+)-binding protein
     that is exported without N-terminal cleavage and is homologous to
     haemolysin and related proteins."
     EMBO J. 9:349-354(1990).
     PubMed=2303029
[ 2] Baumann U., Wu S., Flaherty K.M., McKay D.B.
     "Three-dimensional structure of the alkaline protease of Pseudomonas
     aeruginosa: a two-domain protein with a calcium binding parallel beta
     roll motif."
     EMBO J. 12:3357-3364(1993).
     PubMed=8253063

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