A cDNA clone for glutaminyl cyclase was isolated from a human pituitary cDNA library and the complete DNA sequence determined. The cDNA clone had 1573 bp and contained an open reading frame of 1086 bases, coding for a protein of 361 amino acids and molecular mass of 40,876 Da. The predicted amino acid sequence of the human cDNA showed 86% sequence identity to the previously reported bovine glutaminyl cyclase sequence. A comparison of the amino acid sequences derived from the human and bovine cDNAs showed that several glycosylation and phosphorylation sites as well as two cysteine residues (Cys139, Cys164) were conserved. The human cDNA was cloned into the Escherichia coli expression vectors pMALc2 and pET19b. Expression of this cDNA in either vector resulted in the production of a glutaminyl cyclase fusion protein which was enzymatically active and reacted with anti-bovine glutaminyl cyclase antisera. Substrate specificity studies with the recombinant enzyme suggested a bias against acidic and tryptophan residues adjacent to the N-terminal glutaminyl residue and a lack of importance of chain length after the second residue.

We report the cloning of a low-molecular-weight GTP-binding protein that appears to be the first member of a new class of G proteins. This G protein was cloned from the HT4 neural cell line and has the closest homology to the tab, sec4, and yptl members of the low-molecular-weight (LMW) G-protein family. The amino acid sequence identity is only 30% with these other LMW G proteins, but in the four conserved GTP-binding domains, amino acid identity increases to 50-100%. A unique feature that distinguishes this G protein from other LMW G proteins is its carboxy-terminal amino acid sequence -Cys-Cys-Pro. In keeping with the current nomenclature for other members of the ras supedamily, we will designate this new class as rah (ras-related homolog). On the basis of sequence homology, rah may function in vesicular trafficking and possibly in neurotransmitter secretion.