Naomi Kitamura

ANGIOTENSINOGEN AND KININOGEN: CLONING AND SEQUENCE ANALYSIS OF THE cDNAS

The primary structures of the angiotensinogen precursor and the low molecular weight (LMW) kininogen precursors have been deduced by determining the nucleotide sequences of cloned DNAs complementary to their mRNAs. The angiotensinogen precursor consists of a mature angiotensinogen of 453 amino acid residues and a putative signal peptide of 24 amino acid residues. An angiotensin moiety is located at the amino-terminal part of angiotensinogen, preceded directly by the signal peptide and followed by a large carboxyl-terminal sequence that contains two internally homologous sequences and three potential glycosylation sites. The LMW kininogen precursors are encoded by two very similar but distinct mRNAs and composed of 436 and 434 amino acid residues. Both kininogens contain two internally homologous sequences in which all amino acid differences between the two kininogens are located. This suggests that these homologous regions may be biologically significant in relation to the existence of two LMW kininogens.

Control of Kininogen Gene Expression

Kininogens are precursor proteins of bradykinin that are widely distributed in mammalian blood plasma1-3. Kininogens are comprised of two distinct proteins, designated low molecular weight (LMW) and high molecular weight (HMW) kininogens. Both kininogens are single-chain glycoproteins and carry a bradykinin moiety in the interior of the polypeptide chains bridged by a disulfide linkage. The kininogens thus consist of three domains: an amino-terminal heavy chain (H chain), bradykinin, and a carboxyl-terminal light chain (L chain). The key functions of kininogens, effected via kinin, are smooth muscle contraction, induction of hypotension, pain generation and increase of vascular permeability. Another well-established kininogen function is related to the initial step of blood coagulation and fibrinolysis, and this function is attributed to the L chain of HMW kininogen. Although the pharmacology, physiology and biochemistry of the kinin-kininogen system have been remarkably developed through studies conducted in a number of laboratories, the molecular and genetic aspects of this system remained to be clarified. Our laboratory is concerned with investigations on the structure, expression and regulation of the kininogen gene with the aid of molecular cloning and its related technology.