Department of Chemistry , The Pennsylvania State University , University Park , Pennsylvania 16802 , United States.
Biochemistry. 2019 Jun 11;58(23):2665-2669. doi: 10.1021/acs.biochem.9b00358. Epub 2019 May 29.
Pyrroloquinoline quinone (PQQ) is an essential redox cofactor in bacterial calcium- and lanthanide-dependent alcohol dehydrogenases. Although certain bacteria are known to synthesize and secrete PQQ, little is known about trafficking of this cofactor within and between cells. Here, we show that a previously uncharacterized periplasmic (solute) binding protein from Methylobacterium extorquens AM1, here renamed PqqT, binds 1 equiv of PQQ with high affinity ( K = 50 nM). UV-visible and spectrofluorometric titrations establish that PqqT binds an unhydrated form of PQQ with distinct spectral features from the cofactor in free solution. To our knowledge, PqqT is the first solute-binding protein identified for PQQ and the first protein implicated in cellular trafficking of the cofactor. We propose that PqqT, which is encoded adjacent to a putative ATP-binding cassette transporter in the M. extorquens genome, is involved in uptake of exogenous PQQ to supplement endogenous cofactor biosynthesis. These results support the emerging importance of PQQ transfer within microbial and microbe-host communities.
吡咯并喹啉醌（PQQ）是细菌中钙和镧系依赖性醇脱氢酶的必需氧化还原辅因子。尽管已知某些细菌能够合成和分泌 PQQ，但对于该辅因子在细胞内和细胞间的运输知之甚少。在这里，我们表明，来自甲基杆菌外毒素 AM1 的一种先前未被表征的周质（溶质）结合蛋白，在这里重新命名为 PqqT，能够高亲和力（K = 50 nM）结合 1 当量的 PQQ。紫外可见和荧光光谱滴定表明，PqqT 结合的 PQQ 形式为未水合形式，与游离溶液中的辅因子具有明显不同的光谱特征。据我们所知，PqqT 是鉴定的第一个 PQQ 溶质结合蛋白，也是第一个与该辅因子的细胞内运输有关的蛋白。我们提出，PqqT 可能参与了外源性 PQQ 的摄取，以补充内源性辅因子的生物合成，PqqT 编码在甲基杆菌基因组中一个假定的 ATP 结合盒转运蛋白的旁边。这些结果支持了 PQQ 在微生物和微生物宿主群落内转移的重要性日益增加。
