Knighton D R, Pearson R B, Sowadski J M, Means A R, Ten Eyck L F, Taylor S S, Kemp B E
Department of Chemistry, University of California San Diego, La Jolla 92093-0654.
Science. 1992 Oct 2;258(5079):130-5. doi: 10.1126/science.1439761.
The smooth muscle myosin light chain kinase (smMLCK) catalytic core was modeled by using the crystallographic coordinates of the cyclic AMP-dependent protein kinase catalytic subunit (cAPK) and a bound pseudosubstrate inhibitor peptide, PKI(5-24). Despite only 30% identity in amino acid sequence, the MLCK sequence can be readily accommodated in this structure. With the exception of the short B-helix, all major elements of secondary structure in the core are very likely conserved. The active site of the modeled MLCK complements the known requirements for peptide substrate recognition. MLCK contains a pseudosubstrate sequence that overlaps the calmodulin binding domain and has been proposed to act as an intrasteric inhibitor and occupy the substrate binding site in the absence of Ca(2+)-calmodulin. The pseudosubstrate sequence can be modeled easily into the entire backbone of PKI(5-24). The results demonstrate that the intrasteric model for regulation of MLCK by intramolecular competitive inhibition is structurally plausible.
利用环磷酸腺苷依赖性蛋白激酶催化亚基（cAPK）和结合的假底物抑制剂肽PKI(5 - 24)的晶体学坐标，对平滑肌肌球蛋白轻链激酶（smMLCK）催化核心进行了建模。尽管氨基酸序列的同一性仅为30%，但MLCK序列仍可轻松适配于该结构。除了短的B - 螺旋外，核心中所有主要的二级结构元件很可能是保守的。所建模的MLCK的活性位点符合肽底物识别的已知要求。MLCK包含一个与钙调蛋白结合域重叠的假底物序列，有人提出它可作为一种分子内抑制剂，在没有Ca(2 +)-钙调蛋白的情况下占据底物结合位点。假底物序列可以很容易地建模到PKI(5 - 24)的整个主链中。结果表明，通过分子内竞争性抑制来调节MLCK的分子内模型在结构上是合理的。
