Design Maps of TRPM8 as a Thermometer for Cold Detection

The menthol sensor TRPM8 can be activated by cold and thus serves as a thermometer in a primary afferent sensory neuron for noxious cold detection. However, the underlying design principle is unknown. Here, a hairpin topological structural model and graph theory were prepared to test a role of the cold-dependent hairpin formation in the cold-evoked gating pathway of TRPM8. The results showed that the formation of a large lipid-dependent hairpin initiates a low temperature threshold in favor of TRPM8 activation. Furthermore, two smaller hairpins, which enhance the coupled interactions of the voltage-sensor-like domain with both the pore domain and the TRP domain, can stabilize the cold efficacy and work as a fuse to prevent cold denaturation. The cold-induced hairpin rearrangements along the gating pathway may be necessary for the high cold sensitivity. This hairpin model may provide a structural basis for activation of the thermo-gated TRP channels at low temperature.

Aza-Amino Acids Disrupt β-Sheet Secondary Structures

Cα to N substitution in aza-amino acids imposes local conformational constraints, changes in hydrogen bonding properties, and leads to adaptive chirality at the nitrogen atom. These properties can be exploited in mimicry and stabilization of peptide secondary structures and self-assembly. Here, the effect of a single aza-amino acid incorporation located in the upper β-strand at a hydrogen-bonded (HB) site of a β-hairpin model peptide (H-Arg-Tyr-Val-Glu-Val-d-Pro-Gly-Orn-Lys-Ile-Leu-Gln-NH2) is reported. Specifically, analogs in which valine3 was substituted for aza-valine3 or aza-glycine3 were synthesized, and their β-hairpin stabilities were examined using Nuclear Magnetic Resonance (NMR) spectroscopy. The azapeptide analogs were found to destabilize β-hairpin formation compared to the parent peptide. The aza-valine3 residue was more disruptive of β-hairpin geometry than its aza-glycine3 counterpart.

High-resolution structures of HIV-1 Gag cleavage mutants determine structural switch for virus maturation

HIV-1 maturation occurs via multiple proteolytic cleavages of the Gag polyprotein, causing rearrangement of the virus particle required for infectivity. Cleavage results in beta-hairpin formation at the N terminus of the CA (capsid) protein and loss of a six-helix bundle formed by the C terminus of CA and the neighboring SP1 peptide. How individual cleavages contribute to changes in protein structure and interactions, and how the mature, conical capsid forms, are poorly understood. Here, we employed cryoelectron tomography to determine morphology and high-resolution CA lattice structures for HIV-1 derivatives in which Gag cleavage sites are mutated. These analyses prompt us to revise current models for the crucial maturation switch. Unlike previously proposed, cleavage on either terminus of CA was sufficient, in principle, for lattice maturation, while complete processing was needed for conical capsid formation. We conclude that destabilization of the six-helix bundle, rather than beta-hairpin formation, represents the main determinant of structural maturation.