| Literature References | 1. FRITZINGER, D.C., PETRELLA, E.C., CONNELLY, M.B., BREDEHORST, R.
AND VOGEL, C.W.
Primary structure of cobra complement component C3.
J.IMMUNOL. 149 3554-3562 (1992).
2. OGATA, R.T., ROSA, P.A. AND ZEPF, N.E.
Sequence of the gene for murine complement component C4.
J.BIOL.CHEM. 264 16565-16572 (1989).
3. GENNARO, R., SIMONIC, T., NEGRI, A., MOTTOLA, C., SECCHI, C., RONCHI, S.
AND ROMEO, D.
C5a fragment of bovine complement. Purification, bioassays, amino-acid
sequence and other structural studies.
EUR.J.BIOCHEMISTRY 155 77-86 (1986).
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| Documentation | Complement components C3, C4 and C5 are large glycoproteins that have
important functions in the immune response and host defence [1]. They have
a wide variety of biological activities and are proteolytically activated
by cleavage at a specific site, forming a- and b-fragments [2]. A-fragments
form distinct structural domains of approximately 76 amino acids, coded for
by a single exon within the complement protein gene. The C3a, C4a and C5a
components are referred to as anaphylatoxins [2,3]: they cause smooth muscle
contraction, histamine release from mast cells, and enhanced vascular
permeability [3]; they also mediate chemotaxis, inflammation, and generation
of cytotoxic oxygen radicals [3]. The proteins are highly hydrophilic, with
a mainly alpha-helical structure held together by 3 disulphide bridges [3].
ANAPHYLATOXN is a 3-element fingerprint that provides a signature for
complement C3a, C4a and C5a anaphylatoxin domains. The fingerprint was
derived from an initial alignment of 6 sequences: the motifs encode
conserved regions containing 6 cysteines involved in disulphide bond
formation. Two iterations on OWL24.0 were required to reach convergence,
at which point a true set comprising 28 sequences was identified.
An update on SPTR37_9f identified a true set of 21 sequences.
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