Evolutionarily Conserved, “Acatalytic” Carbonic Anhydrase-Related Protein XI Contains a Sequence Motif Present in the Neuropeptide Sauvagine: The Human CA-RP XI Gene (CA11) Is Embedded between theSecretorGene Cluster and theDBPGene at 19q13.3

Abstract

Conserved amino acid motifs are found in numerous expressed genes. Proteins and peptides with functional relationships may be identified using probes designed to hybridize with these motifs. An oligonucleotide probe was prepared to match the sequence of the expected active region of a frog corticotropin-releasing factor-like peptide sauvagine and used to screen a sheep brain cDNA library. A novel 1331-bp cDNA encoding a putative 328-residue protein with a theoretical mass of 36 kDa was identified. The presence of a strong signal sequence indicates that it is a secreted protein. The amino- and carboxy-terminal regions are characterized by several potential phosphorylation sites and binding motifs, suggesting a role in intracellular signal transduction. Although the protein possesses a 7-residue sequence identical to that found in sauvagine, its overall primary structure most closely resembles those of the α-carbonic anhydrases (α-CAs). Moreover, the detection of the human and mouse orthologues in the EST databases, together with an evolutionary analysis, indicates that the protein represents a new member of the α-CA gene family, which we designate carbonic anhydrase-related protein XI (CA-RP XI), encoded byCA11(human) andCar11(mouse, rat). The humanCA11gene appears to be located between the secretor type α(1,2)-fucosyltransferase gene cluster (FUT1–FUT2–FUT2P) and the D-site binding protein gene (DBP) on chromosome 19q13.3. Despite potentially inactivating changes in the active-site residues, CA-RP XI is evolving very slowly in mammals, a property indicative of an important function, which has also been observed in the two other “acatalytic” CA isoforms, CA-RP VIII and CA-RP X, whose functions are unknown.