Stott Katherine, Watson Matthew, Bostock Mark J, Mortensen Simon A, Travers Andrew, Grasser Klaus D, Thomas Jean O
From the Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA, United Kingdom and.
the Department of Cell Biology and Plant Biochemistry, Biochemie-Zentrum Regensburg, University of Regensburg, Universitätsstrasse 31, 93053 Regensburg, Germany.
J Biol Chem. 2014 Oct 24;289(43):29817-26. doi: 10.1074/jbc.M114.591115. Epub 2014 Sep 4.
The Drosophila and plant (maize) functional counterparts of the abundant vertebrate chromosomal protein HMGB1 (HMG-D and ZmHMGB1, respectively) differ from HMGB1 in having a single HMG box, as well as basic and acidic flanking regions that vary greatly in length and charge. We show that despite these variations, HMG-D and ZmHMGB1 exist in dynamic assemblies in which the basic HMG boxes and linkers associate with their intrinsically disordered, predominantly acidic, tails in a manner analogous to that observed previously for HMGB1. The DNA-binding surfaces of the boxes and linkers are occluded in "auto-inhibited" forms of the protein, which are in equilibrium with transient, more open structures that are "binding-competent." This strongly suggests that the mechanism of auto-inhibition may be a general one. HMG-D and ZmHMGB1 differ from HMGB1 in having phosphorylation sites in their tail and linker regions. In both cases, in vitro phosphorylation of serine residues within the acidic tail stabilizes the assembled form, suggesting another level of regulation for interaction with DNA, chromatin, and other proteins that is not possible for the uniformly acidic (hence unphosphorylatable) tail of HMGB1.
丰富的脊椎动物染色体蛋白HMGB1在果蝇和植物（玉米）中的功能对应物（分别为HMG-D和ZmHMGB1）与HMGB1不同，它们只有一个HMG框，以及长度和电荷差异很大的碱性和酸性侧翼区域。我们发现，尽管存在这些差异，HMG-D和ZmHMGB1仍以动态组装形式存在，其中碱性HMG框和连接子与其内在无序、主要为酸性的尾部相互作用，其方式类似于之前观察到的HMGB1的相互作用方式。在蛋白质的“自抑制”形式中，框和连接子的DNA结合表面被封闭，这些形式与短暂的、更开放的“具有结合能力”的结构处于平衡状态。这有力地表明自抑制机制可能是一种普遍机制。HMG-D和ZmHMGB1与HMGB1的不同之处在于其尾部和连接子区域有磷酸化位点。在这两种情况下，酸性尾部丝氨酸残基的体外磷酸化稳定了组装形式，这表明与DNA、染色质和其他蛋白质相互作用存在另一种调控水平，而这对于HMGB1均匀酸性（因此不可磷酸化）的尾部来说是不可能的。
