Thompson N T, Bonser R W, Hodson H F, Garland L G
Department of Biochemical Sciences, Wellcome Research Laboratories, Kent, U.K.
Biochem J. 1988 Oct 15;255(2):417-22. doi: 10.1042/bj2550417.
The activity of the Ca2+- and phospholipid-dependent protein kinase, protein kinase C (PKC), can be modulated by diacylglycerols and phorbol esters. The association of these agents with PKC is, in turn, generally understood to be dependent on Ca2+ and phospholipids. Certain substrates, e.g. protamine sulphate, are known to undergo cofactor-independent phosphorylation by PKC. We report here that, in the presence of such substrates, PKC bound 1,2-dihexanoylglycerol and phorbol dibutyrate in a Ca2+-independent manner. Histone IIIs, which is phosphorylated by PKC only in the presence of Ca2+ and phospholipid, also supported Ca2+-independent binding of 1,2-dihexanoylglycerol and phorbol dibutyrate to PKC, but to a lesser extent than did protamine. Support for Ca2+-independent binding was also exhibited by non-peptide polycations (e.g. DEAE-cellulose DE52), indicating that recognition of the catalytic site is not a prerequisite for this effect. The natural polyamines spermine and putrescine did not have this property, however. The affinity of PKC for phorbol dibutyrate and 1,2-dihexanoylglycerol was found to be unchanged by the presence of substrates or DE52. It is proposed that, in the absence of Ca2+, certain polycations favour expression of the diacylglycerol/phorbol ester binding site by stabilizing the active conformation of PKC.
钙离子和磷脂依赖性蛋白激酶，即蛋白激酶C（PKC）的活性可被二酰基甘油和佛波酯调节。反过来，通常认为这些物质与PKC的结合依赖于钙离子和磷脂。已知某些底物，如硫酸鱼精蛋白，可被PKC进行不依赖辅因子的磷酸化。我们在此报告，在存在此类底物的情况下，PKC以不依赖钙离子的方式结合1,2 - 二己酰甘油和佛波酯。组蛋白IIIs仅在钙离子和磷脂存在时被PKC磷酸化，它也支持1,2 - 二己酰甘油和佛波酯以不依赖钙离子的方式与PKC结合，但程度低于鱼精蛋白。非肽多阳离子（如DEAE - 纤维素DE52）也表现出对不依赖钙离子结合的支持，这表明识别催化位点不是这种效应的先决条件。然而，天然多胺精胺和腐胺不具有此特性。发现底物或DE52的存在不会改变PKC对佛波酯和1,2 - 二己酰甘油的亲和力。有人提出，在没有钙离子的情况下，某些多阳离子通过稳定PKC的活性构象有利于二酰基甘油/佛波酯结合位点的表达。
