George Lorimer - Academia.edu (original) (raw)

Papers by George Lorimer

The Journal of Biological Chemistry, 1991

Biochemistry, 1971

When spinach leaves were exposed t o a n atmosphere of ['*O]oxygen the label was rapidly incorpor... more When spinach leaves were exposed t o a n atmosphere of ['*O]oxygen the label was rapidly incorporated into the carboxyl groups of glycine and serine. This incorporation occurred only in the light. No label was incorporated into the hydroxyl group of serine. Under the same conditions, glycerate and phosphoglycerate did not become labeled. The data are

Science, Apr 30, 1999

The ability of the GroEL chaperonin to unfold a protein trapped in a misfolded condition was dete... more The ability of the GroEL chaperonin to unfold a protein trapped in a misfolded condition was detected and studied by hydrogen exchange. The GroEL-induced unfolding of its substrate protein is only partial, requires the complete chaperonin system, and is accomplished within the 13 seconds required for a single system turnover. The binding of nucleoside triphosphate provides the energy for a single unfolding event; multiple turnovers require adenosine triphosphate hydrolysis. The substrate protein is released on each turnover even if it has not yet refolded to the native state. These results suggest that GroEL helps partly folded but blocked proteins to fold by causing them first to partially unfold. The structure of GroEL seems well suited to generate the nonspecific mechanical stretching force required for forceful protein unfolding. The GroEL chaperonin (1, 2) captures non-native proteins by means of a ring of hydrophobic residues that line the entrance to the central cavity of its heptameric ring (Fig. 1) (3). When GroEL binds adenosine triphosphate (ATP) and the GroES cochaperonin, a massive structure change doubles the GroEL cavity volume and occludes its hydrophobic binding surface (4, 5). Spectroscopic evidence (6, 7), proteinase protection experiments (6, 8), and electron microscopy (4, 9) leave no doubt that the substrate protein is transiently encapsulated in the central cavity under the GroES lid. However, despite much additional structural and biochemical study (1, 2), the manner in which the GroEL structure change promotes protein folding remains to be demonstrated.

Journal of Inorganic Biochemistry

Journal of Biological Chemistry, 1980

Hydrogen peroxide inhibited both carboxylase and oxygenase activities of purified, and fully acti... more Hydrogen peroxide inhibited both carboxylase and oxygenase activities of purified, and fully activated, spinach ribulose-1,5-bisphosphate (RuP2) carboxylase-oxygenase. Inhibition of the carboxylase reaction was mixed competitive with respect to CO2 (Ki = 1.2 mM) and uncompetitive with respect to RuP2. For the oxygenase reaction, H2O2 was a competitive inhibitor with respect to O2 (Ki = 2.1 mM) and an uncompetitive inhibitor with respect to RuP2. H2O2 did not alter the stoichiometry between CO2 and RuP2 in the carboxylase reaction, indicating that H2O2 was not itself a substrate for the enzyme. RuP2 decreased the rate of deactivation of the enzyme which occurred at limiting CO2 concentrations. H2O2 greatly enhanced this stabilizing effect of RuP2 but had no effect on the rate of deactivation in the absence of RuP2. The inhibitory and stabilizing effects of H2O2 varied similarly with H2O2 concentration. These instantaneous, reversible effects of H2O2 were readily distinguishable from an irreversible inhibitory effect which occurred quite slowly, and in the absence of RuP2. These observations are discussed in relation to the enzyme's catalytic mechanism and its activation-deactivation transformations.

Chemical Reviews, 2019

Allosteric signaling in biological molecules, which may be viewed as specific action at a distanc... more Allosteric signaling in biological molecules, which may be viewed as specific action at a distance due to localized perturbation upon binding of ligands or changes in environmental cues, is pervasive in biology. Insightful phenomenological MWC and KNF models galvanized research in describing allosteric transitions for over five decades, and these models continue to be the basis for describing the mechanisms of allostery in a bewildering array of systems. However, understanding allosteric signaling and the associated dynamics between distinct allosteric states at the molecular level is challenging, and requires novel experiments complemented by computational studies. In this review, we first describe symmetry and rigidity as essential requirements for allosteric proteins or multisubunit structures. The general features, with MWC and KNF as two extreme scenarios, emerge when allosteric signaling is viewed from an energy landscape perspective. To go beyond the general theories, we describe computational tools that are either based solely on multiple sequences or their structures to predict the allostery wiring diagram. These methods could be used to predict the network of residues that carry allosteric signals. Methods to obtain molecular insights into the dynamics of allosteric transitions are briefly mentioned. The utility of the methods is illustrated by applications to systems ranging from monomeric proteins in which there is little conformational change in the transition between two allosteric states to membrane bound G-protein coupled receptors, and multisubunit proteins. Finally, the role allostery plays in the functions of ATP-consuming molecular machines, bacterial chaperonin GroEL and molecular motors, is described. Although universal molecular principles governing allosteric signaling do not exist, we can draw the following general conclusions from a survey of different systems. (1) Multiple pathways connecting allosteric states are highly heterogeneous. (2) Allosteric signaling is exquisitely sensitive to the specific architecture of the system, which implies that the capacity for allostery is encoded in the structure itself. (3) The mechanical modes that connect distinct allosteric states are robust to sequence variations. (4) Extensive investigations of allostery in Hemoglobin and more recently GroEL, show that to a large extent a network 2 of salt-bridge rearrangements serves as allosteric switches. In both these examples the dynamical changes in the allosteric switches are related to function.

The EMBO Journal, 1990

Communicated by C.I.Branden Truncations of the subunit of ribulose bisphosphate carboxylase/oxyge... more Communicated by C.I.Branden Truncations of the subunit of ribulose bisphosphate carboxylase/oxygenase (Rubisco) from Rhodospirillum rubrum were generated by site-directed mutagenesis to examine the role of the C-terminal tail section. Removal of the last and the penultimate a-helices in the tail section changes the quaternary structure of the protein. Electrophoretic and electron microscope analysis revealed that the truncated subunits assemble into an octamer, whereas the wild-type enzyme has a dimeric structure. The octomerization of the mutant protein is due to a hydrophobic patch exposed to the solvent by truncation of the subunit. The mutant protein thus consists of four dimers, bound end-to-end by hydrophobic interactions. Insertion of a polar amino acid in the hydrophobic patch by a L424 to N424 substitution restores the familiar dimeric structure. Truncation of the subunit is associated with a considerable decrease in catalytic activity. The mutants undergo carbamylation but bind the reaction intermediate analog, 2-carboxy arabinitol-1,5-bisphosphate, poorly. This indicates that loss of activity in the mutant is due to weakened substrate binding. These findings suggest that the mutations in the tail section of the subunit are transmitted to the active site, although the C-terminal region is far from the active site. On the basis of the crystal structure of Rubisco, we propose a model for how the truncations of the enzyme subunit induce conformational changes in one of the two phosphate binding sites.

The FASEB Journal, 1996

In vitro the chaperonin proteins, GroEL and GroES, facilitate the folding of some other proteins ... more In vitro the chaperonin proteins, GroEL and GroES, facilitate the folding of some other proteins under conditions where that process does not occur spontaneously. Using values drawn from a number of such in vitro studies, together with the known rates of in vivo protein synthesis by Eseherichia coli and the known quantities of GroEL and GroES in E. coli, an assessment of the general role of these proteins in protein folding in vivo has been made. Three specific cases are examined, where compelling evidence points to the involvement of the chaperonins; the in vivo folding of the bacteriophage coat protein during the burst phase of phage morphogenesis and of Rubisco during chloroplast development and during expression of recombinant Rubisco in E. coli. In each case the maximum in vitro rates are nearly sufficient to account for the observed in vivo rates of formation of the native protein. However, in general, there appears to be sufficient GroEL and GroES to facilitate the folding of no more than 5% of all of the proteins within E. coli.-Lorimer, G. H. A quantitative assessment of the role of the chaperonin proteins in protein folding in vivo. FASEBJ. 10, 5-9 (1996)

Protein Folding, 1993

... Molecular Chaperones and Their Role in Protein Assembly Saskia M. van der Vies1, Anthony A. G... more ... Molecular Chaperones and Their Role in Protein Assembly Saskia M. van der Vies1, Anthony A. Gatenby2, Paul V. Viitanen2, and George H. Lorimer2 ... 68. Buchner, J.; Schmidt, M.; Fuchs, M.; Jaenicke, R.; Rudolph, R.; Schmid, FX; Kiefhaber, T. Biochemistry 1991, 30, 1586. 69. ...

Photosynthesis, 1987

Publisher Summary D-ribulose 1,5-bisphosphate carboxylase-oxygenase's (Rubisco) central role ... more Publisher Summary D-ribulose 1,5-bisphosphate carboxylase-oxygenase's (Rubisco) central role in photosynthesis and photorespiration makes it a likely candidate for regulation, though whether it is more or less regulated than other photosynthetic enzymes remains to be seen. Rubisco's activity in vivo certainly seems to be tightly controlled, very probably by a multiplicity of mechanisms. This chapter discusses the recent advances in the understanding of Rubisco, its mechanisms of catalysis and regulation, the synthesis and assembly of its subunits, and the role of interactions between them. The only function that the glycolate pathway seems to serve is to salvage three-quarters of the carbon diverted from photosynthesis by RuBP oxygenase as phosphoglycolate. In doing so, it consumes energy in the form of ATP and reducing equivalents. Such energy consumption may be advantageous in some circumstances. For example, it may dissipate excess photosynthetic reductant under photo-inhibitory conditions associated with CO2 limitation. Rubisco stands at the interface between the inorganic and organic phases of the biosphere's carbon cycle, catalyzing the only reaction by which atmospheric CO2 may be acquired by living organisms.

Photosynthesis, 1981

Publisher Summary This chapter describes the C2 chemo- and photorespiratory carbon oxidation cycl... more Publisher Summary This chapter describes the C2 chemo- and photorespiratory carbon oxidation cycle. All lithotrophic organisms—chemolithotrophic or photolithotrophic—share a common mechanism for the reduction of CO2 to carbohydrate. The oxidation of inorganic substrates is coupled, through NADPH and ATP, to the reduction of CO2 to carbohydrate. The most common mechanism for the reduction of CO2 is the C3 photo- or chemosynthetic carbon reduction cycle (C3 cycle). Hydrogen atoms derived from water are incorporated during all three phases, carboxylation→ reduction→ regeneration, of the C3 cycle. The operation of the C2 cycle results in the consumption of ATP and reducing equivalents. Dark respiration involves both substrate level and oxidative phosphorylation so that 35–40 % of the energy available from the oxidation of glucose is conserved in the form of ATP. There is no net conservation of energy associated with the C2 cycle. On the contrary, an input of energy is required to drive the C2 cycle.

ACS Symposium Series, 1993

... Anthony A. Gatenby, Gail K. Donaldson, François Baneyx, George H. Lorimer, Paul V. Viitanen, ... more ... Anthony A. Gatenby, Gail K. Donaldson, François Baneyx, George H. Lorimer, Paul V. Viitanen, and Saskia M. van der Vies ... 51. Buchner, J.; Schmidt, M.; Fuchs, M.; Jaenicke, R.; Rudolph, R.; Schmid, F. X.; Kiefhaber, T. Biochemistry 1991, 30, 1586. 52. ...

Plant Molecular Biology, 1987

Current Research in Photosynthesis, 1990

Recent progress in in vitro genetic manipulations (1), and in the structural analysis of Rubisco ... more Recent progress in in vitro genetic manipulations (1), and in the structural analysis of Rubisco (2,3) have provided the basis for a rationale mutagenesis of this key enzyme in the photosynthetic carbon metabolism, in attempts to define structure/function relationships. In combination with a better knowledge in the chemistry of the enzymatic reactions, studies of specific changes of highly conserved residues within the active site have been developed. So far, the role of at least two residues essential for activation (Lys 191 in Rhodospirillum rubrum Rubisco) or catalysis (Lys 166) have been defined (4,5). Another strategy consists to examine the functional importance of peptide regions of low homology. Construction of chimaeric genes by sequence replacement have indicated the critical requirement of some regions of the large subunit (i.e. N-terminus, bridge region between N- and C-terminal domains) for the assembly and/or function of the protein (6,7). A similar approach was used here to investigate the role of the C-terminus of the large subunit. Sequence deletion in the tail domain was performed on the gene coding for R.rubrum Rubisco. Mutation was designed to remove the last and pen-ultimate α-helices from the C-terminal extension (Fig.l).

European Journal of Biochemistry, 1978

Proceedings of the National Academy of Sciences, 2003

Biochemistry, 1981

The activated and catalytically competent form of ribulose-1,5-bisphosphate carboxylase is a tern... more The activated and catalytically competent form of ribulose-1,5-bisphosphate carboxylase is a ternary complex of enzymeactivator CO2.Mg. The effectors NADPH and 6-phosphogluconate promoted activation by formation of a rapid equilibrium quaternary complex of enzyme.activator C02.Mg.effector; i.e., the effectors did not activate the enzyme per se but promoted the basic activation process by stabilizing the activated enzymeactivator C02.Mg complex. Kinetic and gel filtration studies showed that the effectors stabilized the binding of the activator C 0 2 and Mg2+ (or Mn2+), thereby decreasing the rate of deactivation. Binding studies indicated the presence of one 6-phosphogluconate binding site per protomer. The binding of 6-phosphogluconate and NADPH to the enzymeactivator C02-Mg complex was (a) completely prevented when the catalytic site for ribulose bisphosphate was Previous studies (Lorimer et al., 1976, 1977; Miziorko & Mildvan, 1974) established that the activation of ribulose 1,5-bisphosphate (RuBP)' carboxylase involves the ordered addition of C 0 2 and Mg2+, with the addition of C 0 2 being the rate-determining step (eq 1). Kinetic turnover (Lorimer,