Salt-induced folding of a rabbit muscle pyruvate kinase intermediate at alkaline pH

A critical review of the role of M2PYK in the Warburg effect

It is becoming generally accepted in recent literature that the Warburg effect in cancer depends on inhibition of M₂PYK, the pyruvate kinase isozyme most commonly expressed in tumors. We remain skeptical. There continues to be a general lack of solid experimental evidence for the underlying idea that a bottle neck in aerobic glycolysis at the level of M₂PYK results in an expanded pool of glycolytic intermediates (which are thought to serve as building blocks necessary for proliferation and growth of cancer cells). If a bottle neck at M₂PYK exists, then the remarkable increase in lactate production by cancer cells is a paradox, particularly since a high percentage of the carbons of lactate originate from glucose. The finding that pyruvate kinase activity is invariantly increased rather than decreased in cancer undermines the logic of the M₂PYK bottle neck, but is consistent with high lactate production. The "inactive" state of M₂PYK in cancer is often described as a dimer (with reduced substrate affinity) that has dissociated from an active tetramer of M₂PYK. Although M₂PYK clearly dissociates easier than other isozymes of pyruvate kinase, it is not clear that dissociation of the tetramer occurs in vivo when ligands are present that promote tetramer formation. Furthermore, it is also not clear whether the dissociated dimer retains any activity at all. A number of non-canonical functions for M₂PYK have been proposed, all of which can be challenged by the finding that not all cancer cell types are dependent on M₂PYK expression. Additional in-depth studies of the Warburg effect and specifically of the possible regulatory role of M₂PYK in the Warburg effect are needed.

Metal-Binding Properties of a Dicysteine-Containing Motif in Protein Tyrosine Kinases

Studying the structural consequences of the direct binding of arsenite, cadmium, cobalt, nickel, and lead to a number of protein tyrosine kinases led to the discovery of the metal-binding properties of a dicysteine-containing motif in the C-terminal (CT) lobe of the kinases. Of all the synthesized peptides derived from different domains of c-Src and Csk, only peptides based on a dicysteine-containing motif located in the CT lobe of the kinase domain-CPESLHDLMCQC and CPESLHDLMC in c-Src, and CPPAVYDVMKNC in Csk-exhibited significant conformational changes in the presence of all metals, as shown by circular dichroism (CD) analyses. Furthermore, CD analysis of natural enzymes c-Src, Csk, Fyn, c-Abl, Lck, EGFR, and c-Src domains containing the CT lobe in the presence of metals showed a significant concentration-dependent conformational change. ICP-MS, (113)Cd NMR, (33)S NMR, and/or molecular modeling studies of CPESLHDLMC and CPPAVYDVMKNC confirmed the binding between the free sulfhydryl groups of the cysteine residues and Cd(II) or As(III). UV-titration studies suggested a high-affinity interaction between Cd(II) and As(III) and the peptides (K(d) values in the range of 0.6-18.3 nM).

Effect of pH on the pore forming activity and conformational stability of ostreolysin, a lipid raft-binding protein from the edible mushroom Pleurotus ostreatus

Ostreolysin, a pore-forming protein from the edible oyster mushroom (Pleurotus ostreatus), is a member of the aegerolysin protein family, a novel group of small acidic proteins found in bacteria, molds, mushrooms, and plants. It binds to lipid rafts and interacts specifically with cholesterol-rich lipid domains. In this study, ostreolysin was classified as a single-domain all-beta-structured protein on the basis of cDNA sequencing. pH-induced and thermally induced unfolding of ostreolysin was studied by means of CD, UV absorption, and intrinsic tryptophan fluorescence to characterize conformational transitions associated with its functional properties, i.e., binding to lipid membranes, pore forming activity on lipid vesicles, and hemolysis. At 25 degrees C and between pH 6 and 9, ostreolysin adopted a monomeric and thermodynamically stable nativelike conformation, characterized by rigid tertiary structure and predominantly beta-sheet secondary structure. Between pH 2 and 3, the protein underwent an irreversible transition to a partially unfolded, molten globule-like state which bound ANS, and exhibited disrupted tertiary structure and enhanced non-native alpha-helical structure. Functional studies showed that, unlike colicins and some other bacterial pore-forming toxins, the acid-induced molten globule-like state of ostreolysin is not relevant for lipid binding and pore formation. Instead, the compact native state was necessary for binding to cholesterol/sphingomyelin multilamellar vesicles, optimally in the pH range from 6 to 7, and for pore formation and hemolysis, maximally between pH 7 and 8.

The Oxidative Folding Rate of Bovine Pancreatic Ribonuclease Is Enhanced by a Covalently Attached Oligosaccharide

Bovine pancreatic ribonuclease B (RNase B) differs from RNase A by the presence of an oligosaccharide moiety covalently attached to Asn 34. Oxidative folding studies of RNase B were carried out at different temperatures using DTT(ox) as the oxidizing agent, and the results were compared with those for RNase A. The oxidative folding rates of RNase B are between 1.7 and 1.3 times faster than those of RNase A at the temperatures that were investigated. The folding pathways of RNase B were determined to be similar to those of RNase A in that two structured intermediates, each lacking one native disulfide bond, were found to populate the regeneration pathways at 25 degrees C and pH 8.3. The thermodynamic stabilities of these two glycosylated intermediates, and their rates of formation from their unstructured precursors in the rate-determining step, were found to be higher than those of their unglycosylated counterparts from RNase A. Thus, the underlying cause for the faster rate of oxidative regeneration of native RNase B appears to be both thermodynamic and kinetic due to the higher stability, and faster rate of formation, of the intermediates of RNase B compared to those of RNase A.