Our Research

                                                                 Despite more than half a century of detailed studies, we still do not have a satisfactory

                                                             physical model for the enormous rate accelerations brought about by enzymes. The Klinman

                                                                                 group focuses on the following three aspects of this problem:

                                       Hydrogen Tunneling, Methyl Transfer and Protein Dynamics

                                                          What is the direct link between protein dynamical motions and the efficiency of the chemical steps

                                                               catalyzed by enzymes? These studies are focused on two fundamental processes in nature:

                                                            hydrogen transfer (shown to occur by quantum mechanical tunneling) that is mediated by the

                                                           heavy atoms of protein and, more recently, methyl group transfer. A model is emerging in which

                                                               a conformational landscape involving motions, both distal and proximal, to the active site, leads

                                                                          to the transient generation of a family of compressed active site configurations.

 

                                                                                                     

                                                               A representation of a subunit of a thermophilic alcohol dehydrogenase illustrating the local

                                                                     protein motions (reorganization) and distal motions (pre-organization) that control

                                                                     efficient H-tunneling. (Klinman (2009) Chem Phys Lett - Frontiers 471, 179-193).

 

                                                             Protein- and Peptide-Derived Cofactors

                                                                Post-translational modifications abound in biology, with a very large number of these reactions

                                                                     involving amino acid side chains. While reversible protein modifications play key roles in

                                                                  cellular regulation, there are numerous unidirectional modifications that occur in the production

                                                                  of bacterial secondary metabolites and in the biogenesis of cofactors. Our group is focused on

                                                             the range of novel enzymatic processes that generate the peptide and protein-derived quinocofactors.

 

                                                                                                        

                                                                           Illustration of the five known protein- and peptide-derived quinocofactors. The four

                                                                       derived from proteins are TPQ, LTQ, TTQ and CTQ. PQQ is the sole post-translational

                                                                         process that occurs on a peptide. (Mure, Mills and Klinman (2000) Biochemistry 41,

                                                                                     9269-9278; Wecksler et al. (2009) Biochemistry 48, 10151-10161).

 

                                                                             Oxygen Activation

                                                           How did organisms cope with the transition from anaerobic to aerobic life? Key issues are determining

                                                          whether there are specific pathways for migration of molecular oxygen to enzyme active sites, the nature

                                                            of persistent chemical intermediates formed from oxygen, and, most importantly, how these chemical

                                                             intermediates are protected from performing undesirable side reactions that would either inactivate the

                                                            protein or lead to poor yield of product. As the major catalysts within cells, enzymes have had to cope

                                                                  with reactive oxygen intermediates that can wreak havoc with protein structure and function.

 

                                                                                                              

                                                                                             A scheme for the 4e¯, 4H+ reduction of O2 to produce H2O.

                                                                                                The potentially damaging species are •OH > O•¯ H2O2.

                                                                                                       (Klinman (2007) Acc Chem Res 40, 325-333).