The inter-alpha-inhibitor family: From structure to regulation

Inter-a-inhibitor (I alpha I) and related molecules, collectively referred to as the I alpha I family, are a group of plasma protease inhibitors. They display attractive features such as precursor polypeptides that give rise to mature chains with quite distinct fates and functions, and inter-chain glycosaminoglycan bonds within the various molecules. The discovery of an ever growing number of such molecules has raised pertinent questions about their pathophysiological functions. The knowledge of this family has long been structure-oriented, whereas the structure/function and structure/regulation relationships of the family members and their genes have been largely ignored. These relationships are now being elucidated in events such as gene transcription, precursor processing, changes in plasma protein levels in health and disease and binding capacities that involve hyaluronan as well as other plasma proteins as ligands. This review presents some recent progress made in these fields that paves the way for an understanding of the functions of I alpha I family members in vivo. Finally, given the wealth of heterogeneous, complicated and sometimes contradictory nomenclatures and acronyms currently in use for this family, a new, uniform, nomenclature is proposed for I alpha I family genes, precursor polypeptides and assembled proteins.