Motivated by several long-lasting mechanistic questions for biomolecular proton pumps,we have engaged in developing hybrid quantum mechanical/molecular mechanical(QM/MM) methods that allow an efficient and reliable description of long-range proton transport in transmembrane proteins.In this review,we briefly discuss several relevant issues:the need to develop a “multi-scale” generalized solvent boundary potential(GSBP) for the analysis of chemical events in large trans-membrane proteins,approaches to validate such a protocol,and the importance of improving the flexibility of QM/MM Hamiltonian.Several recent studies of model and realistic protein systems are also discussed to help put the discussions into context.Collectively,these studies suggest that the QM/MM-GSBP framework based on an approximate density functional theory(SCC-DFTB) as QM holds the promise to strike the proper balance between computational efficiency,accuracy and generality.With additional improvements in the methodology and recent developments by others,especially powerful sampling techniques,this “multi-scale” framework will be able to help unlock the secrets of proton pumps and other biomolecular machines. Motivated by several long-lasting mechanistic questions for biomolecular proton pumps, we have engaged in developing hybrid quantum mechanical / molecular mechanical (QM / MM) methods that allow an efficient and reliable description of long-range proton transport in transmembrane proteins. In this review , we briefly discuss several relevant issues: the need to develop a “multi-scale” generalized solvent boundary potential (GSBP) for the analysis of chemical events in large trans-membrane proteins, approaches to validate such a protocol, and the importance of improving the flexibility of QM / MM Hamiltonian. Recent study of model and realistic protein systems are also discussed to help put the discussions into context. Collectively, these studies suggest that the QM / MM-GSBP framework based on an approximate density functional theory (SCC-DFTB) as QM holds the promise to strike the proper balance between computational efficiency, accuracy and generality .With additional improvements in the metho dology and recent developments by others, especially powerful sampling techniques, this “multi-scale ” framework will be able to help unlock the secrets of proton pumps and other biomolecular machines.