Cloning and Characterization of a Novel, Human Cellular Retinaldehyde-binding Protein CRALBP-like (CRALBPL) Gene

Cellular retinaldehyde-binding protein (CRALBP) plays a role in the vertebrate visual process as a substrate-routing protein. It belongs to a widespread lipid-binding SEC14-like protein family. All the members of the family have the lipid-binding domain called CRAL-TRIO. Here we have isolated a new human CRAL-TRIO domain containing a CRALBP-like (CRALBPL) gene from the cDNA library of human adult brain. The CRALBPL gene consisted of 1,694 bp and had an ORF encoding putatively 354 amino acids with a CRAL-TRIO domain from 118 to 279 aa. The expression pattern in 18 human tissues indicated that CRALBPL gene was mainly expressed in brain. The alignment of CRAL-TRIO domain showed that CRALBPL had 45% identity with human CRALBP. Subcellular location revealed that CRALBPL protein was located in the cytoplasm of HeLa cells. Western blotting indicated that the CRALBPL had a molecular weight of about 40 kDa.     

Recombinant SEC14-like proteins (TAP) possess GTPase activity

The three human SEC14-like proteins TAP1, TAP2, and TAP3 were expressed in Escherichia coli and purified by means of an amino-terminal His-tag. The recombinant TAP proteins bound α-, β-, γ-, and δ-tocopherol, certain phospholipids, and squalene. Intriguingly, the TAP proteins showed considerable GTPase activity that was comparable to that of small GTP-binding proteins of the Rab family. Although the TAP proteins contain important motifs to provide GTPase activity, the surrounding secondary structure markedly differed from common G-protein domains. However, these motifs are located in close proximity in the TAP structure and may therefore form an active site for GTP-binding and hydrolysis.