SCHWARZ, R.S.*; CADAVID, L.F.; University of New Mexico, Albuquerque; University of New Mexico, Albuquerque: Immunity in lower Metazoans: characterization of CnPolydom, a pentraxin-containing multidomain protein in Cnidaria

We have identified a novel 352 aa multidomain protein from the hydroid Hydractinia symbiolongicarpus (Cnidaria; Hydrozoa). This protein is encoded in a 5.5 kb genomic region having 6 exons and 5 introns. The protein contains multiple domains including various calcium binding epidermal growth factor (EGF) domains, PAN-apple carbohydrate/protein binding domain, coagulation factor 5/8 C-terminal carbohydrate binding domain and a pentraxin domain, also present in a number of serum proteins and receptors which mediate various immune responses. Such multidomain architecture resembles that of polydom protein from vertebrates which contain a pentraxin domain, von Willebrand factor type A domain, multiple EGF domains and complement control protein domains. Furthermore, in the molecule here described the pentraxin domain shows highest sequence similarity to vertebrate polydom pentraxin domain. We have named this multidomain protein Cnidarian Polydom (CnPolydom). The pentraxin domain from CnPolydom has the signature pentraxin motif (HxCx[S/T]Wx[S/T]) with the substitution of C by A, seen only in polydom pentraxin domains. Phylogenetic analysis of pentraxin domains retrieved from public databases show four distinct clades: (1) the classical short pentraxins including C-reactive protein and serum amyloid P (2) long pentraxins including neuronal pentraxin I and II and apexin (3) pentraxin 3, another long pentraxin member and (4) polydom pentraxins. The CnPolydom pentraxin domain clusters significantly with the polydom clade. Identification of this cnidarian pentraxin represents the most basal pentraxin domain characterized to date and extends the taxonomic distribution of highly conserved pentraxins from cnidarians to vertebrates. CnPolydom may play a role in immunity.