甜菜碱与藻胆蛋白超分子复合体相互作用的分子机制

Molecular mechanisms for interaction of glycine betaine with supra-molecular phycobiliprotein complexes

甘氨酸甜菜碱是具有重要生物学意义的生物小分子,它可以保护细胞、蛋白和酶的结构功能完整性,也会导致蛋白超分子结构松散、功能钝化,这两种相反作用的分子机制尚不清楚.本文以超分子藻胆蛋白和藻胆体为模型,证明甜菜碱导致超分子藻胆体结构松散、各组份能量失耦合,最敏感的作用位点是核-膜连接多肽,其次是杆-核连接多肽.C-藻蓝蛋白三聚体与单体对甜菜碱的相应完全不同,前者结构松散而后者相对聚集.甜菜碱屏蔽静电吸引力导致结构松散但强化基元蛋白之间的疏水作用力是两种相反现象的本质,甜菜碱最终导致C-藻蓝蛋白三聚体和单体相同的光谱特征是两种机制的'折中'.

Glycine betaine （GB） is a biologically important small molecule protecting cells, proteins and enzymes in vivo and in vitro under environmental stresses. Recently, it was found that GB could also relax the structure and inactivate function of phycobiliproteins and phycobilisome （PBS）, a kind of supra-molecular complexes, in cyanobacterial cells. The molecular mechanisms for the opposite phenomena are quite ambiguous. Taking PBS and a trimeric or monomeric C-phycocyanin （C-PC） as models, the molecular mechanism for the interaction of GB with supra-molecular complexes or nuclear proteins was investigated. The energetic decoupling of PBS components induced by GB suggests that the PBS core-membrane linking polypeptide was the most sensitive site while the rod-core linker was the next. Biochemistry analysis proves that PBS structure was loosened but not dissociated into the components. On the basis of the results and structure knowledge, it was proposed that GB screened the electrostatic attraction of the opposite charges on a linker and a protein leading to a much looser structure. It was observed that GB induced a spectral blue shift for trimeric C-PC but a red shift for a monomeric C-PC （a nuclear protein）, which were ascribed to GB＇s screening of the electrostatic attraction of a linker to a protein and strengthening of the hydrophobic interaction between C-PC monomers. The trimers and monomers＇ forming of the same products under high concentration of GB was ascribed to a compromise of the opposite interaction forces.