The archaeal model organism Sulfolobus acidocaldarius possesses a TetR-like transcription factor that represses a 30-kb gene cluster encoding fatty acid metabolism enzymes. Interaction of this regulator, FadR_Sa, with acyl-CoA molecules causes a DNA dissociation, which may lead to a derepression of the gene cluster. Previously, a phosphoproteome analysis revealed the phosphorylation of three consecutive amino acids in the acyl-CoA ligand binding pocket. Here, we study this phosphorylation event and show that ArnC, a Hanks-type protein kinase, targets a threonine within the phosphoacceptor motif in vitro. Electrophoretic mobility shift assays using a phosphomimetic mutant of FadR_Sa demonstrate that the presence of negatively charged groups on the phosphoacceptor motif causes an inhibition of the ligand binding that desensitizes the responsiveness of the regulator to acyl-CoA molecules. Based on these observations, we propose a model in which phosphorylation of FadR_Sa in its ligand-binding pocket acts as an additional regulatory layer silencing acyl-CoA responsive derepression of fatty acid and lipid degradation. Moreover, given the recently discovered interplay between FadR_Sa and the chromosome structuring protein coalescin, FadR_Sa phosphorylation could also influence local chromosome conformation under specific cellular conditions.

原始模型生物Sulfolobus acidocaldarius具有TetR样转录因子，可抑制编码脂肪酸代谢酶的30-kb基因簇。该调节剂FadR _Sa与酰基CoA分子的相互作用导致DNA解离，这可能导致基因簇的抑制。以前，磷酸蛋白质组分析显示了酰基辅酶A配体结合口袋中三个连续氨基酸的磷酸化。在这里，我们研究了这种磷酸化事件，并显示了Hank型蛋白激酶ArnC在体外靶向磷酸化受体基序中的苏氨酸。使用FadR _Sa的磷酸化突变体进行电泳迁移率迁移测定证明了磷酸受体基序上带负电荷的基团的存在引起配体结合的抑制，从而使调节剂对酰基辅酶A分子的响应性降低。基于这些观察结果，我们提出了一个模型，其中FadR _Sa在其配体结合口袋中的磷酸化充当了额外的调节层，从而使脂肪酸的酰基辅酶A响应性抑制和脂质降解降低。此外，鉴于最近发现的FadR _Sa与染色体结构蛋白凝聚素之间的相互作用，FadR _Sa磷酸化也可能影响特定细胞条件下的局部染色体构象。