Molecular characterization of apolipoprotein A-I from the skin mucosa of Cyprinus carpio

Apolipoprotein A-I is the most abundant protein in Cyprinus carpio plasma that plays an important role in lipid transport and protection of the skin by means of its antimicrobial activity. A 527 bp cDNA fragment encoding C terminus part of apoA-I from the skin mucosa of common carp was isolated using RT-PCR. After GenBank database searching, a partial sequence containing a coding sequence (CDS) relating to this gene was found. Overlapping of the cDNA fragment with this CDS allowed us to obtain the full-length sequence including non-coding regions. This sequence has 1170bp including a polyA tail of 18 bp plus 45 and 354 bp at the 3'- and 5'-untranslatedregions, respectively. The complete sequence contained an open reading frame of 256 amino containing 5 amino acid propeptides with a predicted molecular mass of 29.967 kDa and theoretical pI of 6.13.The signal peptide of common carp apoA-I was predicted to have the most likely cleavage site between amino acid positions 17 and 18. Domain analysis of common carp apoA-I showed the conserved domain of Apolipoprotein A1/A4/E between amino acid resides 67 to 251. The similarity search indicated that common carp apoA-I matched apoA protein from the group of fish with 45-77% similarity, but showed relatively low levels of similarity to its mammalian counterparts (20-28%).It was shown that the secondary structure of C. carpio apoA-I consisted of a-helical predominantly amphipathic in nature and was characterized by the presence of thirteen conserved repeats.