Cloning and characterization of the cDNA encoding guinea-pig properdin: a comparison of properdin from three species.

The cDNA sequence encoding properdin was generated from guinea-pig spleen RNA by the reverse transcription-polymerase chain reaction. This sequence was approximately 75% homologous with human and 71% homologous with murine properdin at the nucleic acid level. Guinea-pig properdin had six thrombospondin repeat sequences consisting of about 60 amino acids, each with six cysteine and three tryptophan residues. Additionally, the Valine-Threonine-Cysteine-Glycine sequence, reported to have important cell adhesive properties in malarial circumsporozoite proteins and thrombospondin, was conserved in the properdin sequence of guinea-pigs. Finally, mouse spleen was also examined to complete the sequence determination of the leader peptide and the initial four residues of murine properdin. This allowed a thorough comparison of the primary structure of properdin from all three species. Like human and murine properdin cDNAs, the guinea pig sequence contained a region of unique, non-homologous sequence (18 base pairs in length) within the fifth thrombospondin repeat, the significance of which remains unclear.