Vertebrate patatin-like phospholipase domain-containing protein 4 (PNPLA4) genes and proteins: a gene with a role in retinol metabolism

At least eight families of mammalian patatin-like phospholipase domain-containing proteins (PNPLA) (E.C. 3.1.1.3) catalyse the hydrolysis of triglycerides, including PNPLA4 (alternatively PLPL4 or GS2), which also acts as a retinol transacylase and participates in retinol-ester metabolism in the body. Bioinformatic methods were used to predict the amino acid sequences, secondary and tertiary structures and gene locations for PNPLA4 genes and encoded proteins using data from several vertebrate genome projects. PNPLA4 genes were located on the X-chromosome for the eutherian mammalian genomes examined. Opossum (marsupial), chicken, anole lizard, clawed toad, zebrafish and lancelet PNPLA4 genes were also identified. Most vertebrate PNPLA4 genes typically contained six coding exons whereas the lancelet PNPLA4 gene contained five coding exons. PNPLA4 subunits were the smallest among the PNPLA-like proteins examined containing 252–255 residues, shared >64 % sequence identities and key amino acid residues and predicted motifs, including ‘patatin’ (residues 6–176); putative catalytic dyad active site residues, Ser43 and Asp163; oxy-anion ‘hole’ residues (10–15); and conserved serine residues, which may perform structural roles for this enzyme. Predicted tertiary structures for PNPLA4 ‘patatin’ were similar to those reported for potato ‘patatin’, suggesting that it is strongly conserved during evolution. Human PNPLA4 contained a CpG49 island within the gene promoter, a miRNA-186 binding site within the mRNA 3′-noncoding region for the PNPLA4b isoform and exhibited wide tissue expression at a higher than average level. These and previous studies of vertebrate PNPLA-like gene families have suggested that PNPLA4 is an ancient gene in evolution which has resulted from a duplication of an ancestral invertebrate ATGL-like gene (encoding adipose triglyceride lipase). ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s13205-012-0063-7) contains supplementary material, which is available to authorized users.