Evolution of the mannose-binding lectin gene in primates.

The mannose-binding lectin MBL2 plays an important role in the innate immune system. It binds carbohydrates surface, acts as an opsonin and activates the complement system. With the aim of studying the evolution of the MBL2 gene in primates, we sequenced its coding region in 12 non-human primate species and compared them with the human sequence. We demonstrated that nucleotide and amino-acidic sequences of the MBL2 among primates are highly homologous, underlining the importance of this molecule in the defense system against pathogen invasions. In particular, in the collagen-like domain that confers the characteristic structure to MBL2 protein, the identity among primates is really high. In the carbohydrate recognition domain, we evidenced some primates' group-specific amino-acidic mutations not resulting in changes of the structure or function of this MBL2 domain. Phylogenetic analysis did not evidence any positive selective pressure in MBL2 gene among non-human primates. Our findings indicate that MBL2 is well conserved in agreement with its important role in the immune system: in non-human primates, we did not observe the same 'plasticity' of the MBL2 human gene, where a frequency of more than 1% of nucleotide variations was described in the coding and promoter regions.