Kininogen

Kininogen is a type of protein that plays a crucial role in the blood coagulation system and the kinin-kallikrein system. It is a precursor to kinin, a group of proteins that cause blood vessels to dilate and cause smooth muscle to contract.

Structure

Kininogen is a single-chain glycoprotein that is produced in the liver. It is composed of two types: high molecular weight kininogen (HMWK) and low molecular weight kininogen (LMWK). Both types are encoded by the same gene, but they differ in their post-translational modifications and functions.

Function

Kininogen serves as a precursor to kinin, which is released through the action of kallikrein, an enzyme that cleaves kininogen. Kinin, in turn, is a potent mediator of various physiological processes, including vasodilation, inflammation, and pain perception.

HMWK is involved in blood coagulation, acting as a cofactor for the assembly of the prekallikrein-Factor XII complex. LMWK, on the other hand, is primarily involved in the kinin-kallikrein system, leading to the production of bradykinin, a potent vasodilator.

Clinical significance

Alterations in the levels of kininogen can lead to various health conditions. For instance, reduced levels of HMWK can result in hereditary angioedema, a rare but serious condition characterized by episodes of severe swelling. On the other hand, elevated levels of kininogen have been associated with increased risk of thrombosis and cardiovascular disease.

See also

• Kinin-kallikrein system
• Blood coagulation
• Bradykinin
• Hereditary angioedema