Thermal unfolding and aggregation of actin

Abstract

Actin is one of the most abundant proteins in nature. It is found in all eukaryotes and plays a fundamental role in many diverse and dynamic cellular processes. Also, actin is one of the most ubiquitous proteins because actin‐like proteins have recently been identified in bacteria. Actin filament (F‐actin) is a highly dynamic structure that can exist in different conformational states, and transitions between these states may be important in cytoskeletal dynamics and cell motility. These transitions can be modulated by various factors causing the stabilization or destabilization of actin filaments. In this review, we look at actin stabilization and destabilization as expressed by changes in the thermal stability of actin; specifically, we summarize and analyze the existing data on the thermal unfolding of actin as measured by differential scanning calorimetry. We also analyze in vitro data on the heat‐induced aggregation of actin, the process that normally accompanies actin thermal denaturation. In this respect, we focus on the effects of small heat shock proteins, which can prevent the aggregation of thermally denatured actin with no effect on actin thermal unfolding. As a result, we have proposed a mechanism describing the thermal denaturation and aggregation of F‐actin. This mechanism explains some of the special features of the thermal unfolding of actin filaments, including the effects of their stabilization and destabilization; it can also explain how small heat shock proteins protect the actin cytoskeleton from damage caused by the accumulation of large insoluble aggregates under heat shock conditions.

The proteomic response of cheliped myofibril tissue in the eurythermal porcelain crabPetrolisthes cinctipesto heat shock following acclimation to daily temperature fluctuations

“…At least in the case of cofilin and gelsolin, it seems likely that greater filament depolymerization and severing may increase the susceptibility of actin to partial proteolysis during heat shock. This is consistent with the observation that filamentous actin is much more thermally stable and therefore resistant to partial proteolysis than globular actin (Levitsky et al, 2008).…”

“…Clusters II and III, which showed increased abundance of actin fragments, indicate partial in vivo proteolysis during heat shock. The fact that gels from non-heatshock treatments did not show partial proteolysis suggests that the occurrence of fragments is not an artifact of our sample preparation protocol but is rather due to a low thermal stability intrinsic to actin, which depends on several actin-binding proteins and ATP levels, under in vivo conditions (Levitsky et al, 2008). Also, we observed a similar heat-shock-induced pattern of partial proteolysis for actin isoforms in sea squirts of the genus Ciona (Serafini et al, 2011).…”

Second Harmonic Generation Microscopy: A Tool for Spatially and Temporally Resolved Studies of Heat Induced Structural Changes in Meat

“…Similar methods have been used to study thermal denaturation behavior of myosin [20][21][22] and actin 23,24 . Nevertheless, most of these methods require extraction and solubilization of the protein of interest and are neither applicable for the investigation of complex tissues nor do they allow for simultaneous observation of ongoing structural changes at the required optical resolution.…”

Thermo-mechanical properties of the cell surface assessed by atomic force microscopy

“…The obtained values of T g for erythrocytes and thymocytes were in the intervals of structural-relaxation transition temperatures of spectrin and actin correspondingly. Literature data indicate that the structural-relaxation transitions (unfolding, denaturation) of spectrin and actin occurs in the temperature intervals of 20-80 • C (293-353 K) and 50-80 • C (323-353 K) with the mid-points at 42-50 • C (315-323 K) and 62-67 • C (335-338 K, depending on the relative level of G-/F-actin) correspondingly (Law et al, 2003;An et al, 2006;Levitsky et al, 2008). The transition temperature also depends on the presence of links to other proteins and nucleotides as well as intra-and intermolecular cross-links (Levitsky et al, 2008).…”