Allosteric Control of Three B12-dependent (Class II) Ribonucleotide Reductases IMPLICATIONS FOR THE EVOLUTION OF RIBONUCLEOTIDE REDUCTION

摘要: Three separate classes of ribonucleotide reductases are known, each with a distinct protein structure. One common feature all enzymes is that single generates the four deoxyribonucleotides. Class I and III contain an allosteric substrate specificity site capable binding effectors (ATP or various deoxyribonucleoside triphosphates) direct enzyme specificity. Some (but not all) second binds only ATP dATP. Binding dATP to this inhibits activity these enzymes. X-ray crystallography has localized two sites within structure Escherichia coli class identified effector-binding amino acids. Here, we have studied regulation three II enzymes, one from archaebacterium Thermoplasma acidophilum eubacteria (Lactobacillus leichmannii Thermotoga maritima). Each triphosphates regulates its according same rules as for does inhibit activity, suggesting absence active site. For L. T. maritima experiments also indicate presence Their primary sequences suggest lack structural requirements In contrast, at sites, sequence contains putative acids The without apparent physiological function leads hypothesis functional was present early during evolution reductases, but lost enzyme. other B12 function, basis Also large subgroup (Ib) none investigated This further indirect evidence may arisen by divergent