Bramson H N, Thomas N E, Kaiser E T
J Biol Chem. 1985 Dec 15;260(29):15452-7.
Peptide 1, Leu-Arg-Arg-Ala-Ser-Leu-Gly, is an excellent substrate for cAMP-dependent protein kinase. While the importance of both arginines for effective enzyme-substrate interactions has been shown, it has not been known whether the kinase will catalyze phosphorylation of substrates which contain other than peptide bonds. We report that analogs of peptide 1 which contain depsi linkages replacing selected amide bonds are good protein kinase substrates. Therefore, with the possible exception of the serine amide proton, no peptide 1 amide hydrogens are involved in peptide-peptide or peptide-enzyme hydrogen bonding crucial to defining the high substrate activity of this peptide. It is thus unlikely that peptide 1 is bound by the protein kinase while in an alpha-helical or a beta-turn structure. Three peptides were found to be very poor substrates for protein kinase, those containing N-methyl amino acids in place of Ser5 or Leu6 and a peptide containing Pro in place of Leu6. These peptides are poor substrates for the enzyme possibly because they are unable to adopt a conformation necessary for catalysis of phosphoryl group transfer to occur or due to steric effects in the enzymatic active site.
肽1（Leu-Arg-Arg-Ala-Ser-Leu-Gly）是环磷酸腺苷（cAMP）依赖性蛋白激酶的优良底物。虽然已证明两个精氨酸对于有效的酶-底物相互作用很重要，但尚不清楚该激酶是否会催化含有肽键以外化学键的底物的磷酸化。我们报告称，含有取代特定酰胺键的缩酮连接的肽1类似物是良好的蛋白激酶底物。因此，除了丝氨酸酰胺质子外，肽1的酰胺氢不参与对该肽高底物活性起关键作用的肽-肽或肽-酶氢键形成。因此，肽1在以α-螺旋或β-转角结构存在时不太可能与蛋白激酶结合。发现三种肽是蛋白激酶的非常差的底物，即那些含有N-甲基氨基酸取代Ser5或Leu6的肽以及含有Pro取代Leu6的肽。这些肽是该酶的差底物，可能是因为它们无法采用发生磷酰基转移催化所必需的构象，或者是由于酶活性位点的空间效应。
