Evolutionary History of Cathepsin L (L-like) Family Genes in Vertebrates

Cathepsin L family, an important cysteine protease found in lysosomes, is categorized into cathepsins B, F, H, K, L, S, and W in vertebrates. This categorization is based on their sequence alignment and traditional functional classification, but the evolutionary relationship of family members is unclear. This study determined the evolutionary relationship of cathepsin L family genes in vertebrates through phylogenetic construction. Results showed that cathepsins F, H, S and K, and L and V were chronologically diverged. Tandem-repeat duplication was found to occur in the evolutionary history of cathepsin L family. Cathepsin L in zebrafish, cathepsins S and K in xenopus, and cathepsin L in mice and rats underwent evident tandem-repeat events. Positive selection was detected in cathepsin L-like members in mice and rats, and amino acid sites under positive selection pressure were calculated. Most of these sites appeared at the connection of secondary structures, suggesting that the sites may slightly change spatial structure. Severe positive selection was also observed in cathepsin V (L2) of primates, indicating that this enzyme had some special functions. Our work provided a brief evolutionary history of cathepsin L family and differentiated cathepsins S and K from cathepsin L based on vertebrate appearance. Positive selection was the specific cause of differentiation of cathepsin L family genes, confirming that gene function variation after expansion events was related to interactions with the environment and adaptability.