Two of the three actin-binding domains of gelsolin bind to the same subdomain of actin Implications for capping and severing mechanisms

AbstractGelsolin binds two monomers in the nucleating complex with G-actin in calcium and caps actin filaments. However, 3 actin-binding domains have been identified within its 6 repeating sequence segments corresponding to S1,S2–3 and S4–6, S1 and S4–6 bind only G-actin whereas S2–3 binds specifically to F-actin. Two of the three domains (S2–3 and S4–6) are required for nucleation and a different pair (S1 and S2–3) for severing. Here we show for the first time that the domains unique to nucleation (S4–6) or severing (S1) compete for the same region on subdomain 1 of G-actin. We further show that S2–3 binds actin monomers weakly in G-buffer conditions and that this interaction persists when S1 or S4–6 are also bound. Thus gelsolin associates with two distinct regions on actin. Since S2–3 does not bind monomeric actin in F-buffer, we suggest that its high affinity 1:1 stoichiometry for filament subunits reflects interaction with two adjacent subunits

Changes in myosin light chains in the rat soleus after thyroidectomy

The occurrence of physiological and structural changes in skeletal muscle in hypothyroidism is well-documented..

F-actin and G-actin binding are uncoupled by mutation of conserved tyrosine residues in maize actin depolymerizing factor (ZmADF)

Actin depolymerizing factors (ADF) are stimulus responsive actin cytoskeleton modulating proteins. They bind both monomeric actin (G-actin) and filamentous actin (F-actin) and, under certain conditions, F-actin binding is followed by filament severing. In this paper, using mutant maize ADF3 proteins, we demonstrate that the maize ADF3 binding of F-actin can be spatially distinguished from that of G-actin. One mutant, zmadf3–1, in which Tyr-103 and Ala-104 (equivalent to destrin Tyr-117 and Ala-118) have been replaced by phenylalanine and glycine, respectively, binds more weakly to both G-actin and F-actin compared with maize ADF3. A second mutant, zmadf3–2, in which both Tyr-67 and Tyr-70 are replaced by phenylalanine, shows an affinity for G-actin similar to maize ADF3, but F-actin binding is abolished. The two tyrosines, Tyr-67 and Tyr-70, are in the equivalent position to Tyr-82 and Tyr-85 of destrin, respectively. Using the tertiary structure of destrin, yeast cofilin, and Acanthamoeba actophorin, we discuss the implications of removing the aromatic hydroxyls of Tyr-82 and Tyr-85 (i.e., the effect of substituting phenylalanine for tyrosine) and conclude that Tyr-82 plays a critical role in stabilizing the tertiary structure that is essential for F-actin binding. We propose that this tertiary structure is maintained as a result of a hydrogen bond between the hydroxyl of Tyr-82 and the carbonyl of Tyr-117, which is located in the long α-helix; amino acid components of this helix (Leu-111 to Phe-128) have been implicated in G-actin and F-actin binding. The structures of human destrin and yeast cofilin indicate a hydrogen distance of 2.61 and 2.77 Å, respectively, with corresponding bond angles of 99.5° and 113°, close to the optimum for a strong hydrogen bond

LOSS OF CALCIUM SENSITIVITY OF PLASMA GELSOLIN IS ASSOCIATED WITH THE PRESENCE OF CALCIUM-IONS DURING PREPARATION

POPE B, GOOCH J, Hinssen H, WEEDS AG. LOSS OF CALCIUM SENSITIVITY OF PLASMA GELSOLIN IS ASSOCIATED WITH THE PRESENCE OF CALCIUM-IONS DURING PREPARATION. FEBS LETTERS. 1989;259(1):185-188

Pollen specific expression of maize genes encoding actin depolymerizing factor-like proteins

In pollen development, a dramatic reorganization of the actin cytoskeleton takes place during the passage of the pollen grain into dormancy and on activation of pollen tube growth. A role for actin-binding proteins is implicated and we report here the identification of a small gene family in maize that encodes actin depolymerizing factor (ADF)-like proteins. The ADF group of proteins are believed to control actin polymerization and depolymerization in response to both intracellular and extracellular signals. Two of the maize genes ZmABP1 and ZmABP2 are expressed specifically in pollen and germinating pollen suggesting that the protein products may be involved in pollen actin reorganization. A third gene, ZmABP3, encodes a protein only 56% and 58% identical to ZmABP1 and ZmABP2, respectively, and its expression is suppressed in pollen and germinated pollen. The fundamental biochemical characteristics of the ZmABP proteins has been elucidated using bacterially expressed ZmABP3 protein. This has the ability to bind monomeric actin (G-actin) and filamentous actin (F-actin). Moreover, it decreases the viscosity of polymerized actin solutions consistent with an ability to depolymerize filaments. These biochemical characteristics, taken together with the sequence comparisons, support the inclusion of the ZmABP proteins in the ADF group