Malla Nabin, Berg Eli, Uhlin-Hansen Lars, Winberg Jan-Olof
Department of Medical Biochemistry, Institute of Medical Biology, University of Tromsø, MH Building, Tromsø 9037, Norway.
J Biol Chem. 2008 May 16;283(20):13652-65. doi: 10.1074/jbc.M709140200. Epub 2008 Mar 20.
Previously we have shown that THP-1 cells synthesize matrix metalloproteinase-9 (MMP-9) where a fraction of the enzyme is strongly linked to a proteoglycan (PG) core protein. In the present work we show that these pro-MMP-9.PG heteromers have different biochemical properties compared with the monomeric form of pro-MMP-9. In these heteromers, the fibronectin II-like domain in the catalytic site of the enzyme is hidden, and the fibronectin II-like-mediated binding to gelatin and collagen is prevented. However, a fraction of the pro-MMP-9.PG heteromers interacted with gelatin and collagen. This interaction was not through the chondroitin sulfate (CS) part of the PG molecule but, rather, through a region in the PG core protein, a new site induced by the interaction of pro-MMP-9 and the PG core protein, or a non-CS glycosaminoglycan part of the PG molecule. The interaction between pro-MMP-9.PG heteromers and gelatin was weaker than the interaction between pro-MMP-9 and gelatin. In contrast, collagen I bound to pro-MMP-9.PG heteromers and pro-MMP-9 with approximately the same affinity. Removal of CS chains from the PG part of the heteromers did not affect the binding to gelatin and collagen. Although the identity of the PG core protein is not known, this does not have any impact on the described biochemical properties of the heteromer or its pro-MMP-9 component. It is also shown that a small fraction of the PG, which is not a part of the pro-MMP-9.PG heteromer, can bind gelatin. As for the pro-MMP-9.PG heteromers, this was independent of the CS chains. The structure that mediates the binding of free PG to gelatin is different from the corresponding structure in the pro-MMP-9.PG heteromer, because they were eluted from gelatin-Sepharose columns under totally different conditions. Although only a small amount of pro-MMP-9.PG heteromer is formed, the heteromer may have fundamental physiological importance, because only catalytic amounts of the enzyme are required to digest physiological targets.
此前我们已经表明，THP-1细胞合成基质金属蛋白酶-9（MMP-9），其中一部分酶与蛋白聚糖（PG）核心蛋白紧密相连。在本研究中，我们发现这些前MMP-9.PG异聚体与前MMP-9的单体形式相比具有不同的生化特性。在这些异聚体中，酶催化位点中的纤连蛋白II样结构域被隐藏，纤连蛋白II样介导的与明胶和胶原蛋白的结合被阻止。然而，一部分前MMP-9.PG异聚体与明胶和胶原蛋白相互作用。这种相互作用不是通过PG分子的硫酸软骨素（CS）部分，而是通过PG核心蛋白中的一个区域，即前MMP-9与PG核心蛋白相互作用诱导的新位点，或者PG分子的非CS糖胺聚糖部分。前MMP-9.PG异聚体与明胶之间的相互作用比前MMP-9与明胶之间的相互作用弱。相反，I型胶原蛋白以大致相同的亲和力与前MMP-9.PG异聚体和前MMP-9结合。从异聚体的PG部分去除CS链不会影响与明胶和胶原蛋白的结合。尽管PG核心蛋白的身份尚不清楚，但这对所述异聚体或其前MMP-9组分的生化特性没有任何影响。还表明，一小部分不属于前MMP-9.PG异聚体的PG可以结合明胶。至于前MMP-9.PG异聚体，这与CS链无关。介导游离PG与明胶结合的结构与前MMP-9.PG异聚体中的相应结构不同，因为它们在完全不同的条件下从明胶-琼脂糖柱上洗脱下来。尽管仅形成少量的前MMP-9.PG异聚体，但该异聚体可能具有重要的生理意义，因为仅需催化量的酶就能消化生理靶点。
