A conserved π–cation and an electrostatic bridge are essential for 11R-lipoxygenase catalysis and structural stability

Conflicting Interfacial Electrostatic Interactions as a Design Principle to Modulate Long-Range Interdomain Communication

The extent and molecular basis of interdomain communication in multidomain proteins, central to understanding allostery and function, is an open question. One simple evolutionary strategy could involve the selection of either conflicting or favorable electrostatic interactions across the interface of two closely spaced domains to tune the magnitude of interdomain connectivity. Here, we study a bilobed domain FF34 from the eukaryotic p190A RhoGAP protein to explore one such design principle that mediates interdomain communication. We find that while the individual structural units in wild-type FF34 are marginally coupled, they exhibit distinct intrinsic stabilities and low cooperativity, manifesting as slow folding. The FF3-FF4 interface harbors a frustrated network of highly conserved electrostatic interactions-a charge troika-that promotes the population of multiple, decoupled, and non-native structural modes on a rugged native landscape. Perturbing this network via a charge-reversal mutation not only enhances stability and cooperativity but also dampens the fluctuations globally and speeds up the folding rate by at least an order of magnitude. Our work highlights how a conserved but nonoptimal network of interfacial electrostatic interactions shapes the native ensemble of a bilobed protein, a feature that could be exploited in designing molecular systems with long-range connectivity and enhanced cooperativity.

Fatty Acid Allosteric Regulation of C-H Activation in Plant and Animal Lipoxygenases

Lipoxygenases (LOXs) catalyze the (per) oxidation of fatty acids that serve as important mediators for cell signaling and inflammation. These reactions are initiated by a C-H activation step that is allosterically regulated in plant and animal enzymes. LOXs from higher eukaryotes are equipped with an N-terminal PLAT (Polycystin-1, Lipoxygenase, Alpha-Toxin) domain that has been implicated to bind to small molecule allosteric effectors, which in turn modulate substrate specificity and the rate-limiting steps of catalysis. Herein, the kinetic and structural evidence that describes the allosteric regulation of plant and animal lipoxygenase chemistry by fatty acids and their derivatives are summarized.

Gly188Arg substitution eliminates substrate inhibition in arachidonate 11R-lipoxygenase

Lipoxygenases (LOXs) are dioxygenases that catalyze the oxygenation of polyunsaturated fatty acids to hydroperoxyl derivates. These products are precursors for different lipid mediators which are associated with pathogenesis of various diseases such as asthma, atherosclerosis and cancer. Several LOXs suffer from substrate inhibition, a potential regulatory mechanism, yet it is unclear what is the cause of this phenomenon. One such enzyme is the coral 11R-LOX which displays a significant decrease in turnover rate at arachidonic acid concentrations above 30 μM. In this report, site-directed mutagenesis and inhibition assays were employed to shed light on the mechanism of substrate inhibition in 11R-LOX. We found that introduction of a positive charge to the active site entrance with Gly188Arg substitution completely eliminates the slow-down at higher substrate concentrations. Inhibition of 11R-LOX by its catalysis product, 11(R)-hydroperoxyeicosatetraenoic acid, suggests an uncompetitive mechanism. We reason that substrate inhibition in 11R-LOX is due to additional fatty acid binding by the enzyme:substrate complex at an allosteric site situated in the very vicinity of the active site entrance.