Gonzalez L, Phalip V, Zhang C C
Unité d'Immunotechnologie et Microbiologie Moléculaire, ESBS, Université Louis Pasteur de Strasbourg, Illkirch, France.
Eur J Biochem. 2001 Mar;268(6):1869-75.
Eukaryotic-like protein Ser/Thr and Tyr kinases have only recently been discovered in prokaryotes. In most cases, their biochemical properties have been poorly characterized. The nitrogen-fixing and heterocyst-forming cyanobacterium Anabaena sp. strain PCC 7120 houses a family of eukaryotic-like Ser/Thr kinases. Some of these enzymes are required for cell growth or development under certain conditions. None of them, however, has been shown experimentally to possess Ser/Thr kinase activity. A gene, pknC, encoding a novel putative Ser/Thr kinase was isolated from Anabaena sp. PCC 7120. The recombinant PknC was shown to be phosphorylated on a Thr residue. This phosphorylation was probably due to the autophosphorylation activity of PknC itself because mutation of two amino acid residues within the subdomain II of its catalytic domain eliminated the phosphorylation of PknC. PknC displayed also a Ser kinase activity towards several nonspecific substrates, and the two residues needed for PknC autophosphorylation was equally required for the phosphorylation of other substrates. PknC is thus a Ser/Thr kinase with broad substrate specificity. The activity of PknC is likely to be regulated in vivo in order to limit the spectrum of its substrate specificity.
类真核蛋白丝氨酸/苏氨酸激酶和酪氨酸激酶最近才在原核生物中被发现。在大多数情况下，它们的生化特性尚未得到充分表征。固氮和形成异形胞的蓝藻鱼腥藻属（Anabaena sp.）菌株PCC 7120含有一个类真核丝氨酸/苏氨酸激酶家族。其中一些酶在某些条件下是细胞生长或发育所必需的。然而，它们中没有一个在实验中被证明具有丝氨酸/苏氨酸激酶活性。从鱼腥藻属PCC 7120中分离出一个编码新型假定丝氨酸/苏氨酸激酶的基因pknC。重组PknC在一个苏氨酸残基上被磷酸化。这种磷酸化可能是由于PknC自身的自磷酸化活性，因为其催化结构域亚结构域II内的两个氨基酸残基发生突变消除了PknC的磷酸化。PknC对几种非特异性底物也表现出丝氨酸激酶活性，并且PknC自磷酸化所需的两个残基对于其他底物的磷酸化同样是必需的。因此，PknC是一种具有广泛底物特异性的丝氨酸/苏氨酸激酶。PknC的活性可能在体内受到调节，以限制其底物特异性的范围。
