Dynamic reorganization of the motor domain of myosin subfragment 1 in different nucleotide states

Abstract

, were shown to provide an excellent structural framework for using to understand the mechanism of muscle contraction. According to these D. discoideum structures, S1.ADP.BeF x resembles the S1.ATP conformation, whereas S1.ADP.AlF -4 and S1. ADP.V i resemble the S1.ADP.P i conformation. On the other hand, the smooth muscle myosin S1 atomic structures with ADP.BeF x and ADP.AlF -4 were almost identical [7]. Analysis of these atomic models revealed that a key structural part of the nucleotide induced conformational changes in the core of the motor domain is the switch 2 (SWII) element, which consists of the SWII helix (residues 475-509) and the SWII loop (residues 511-520). The SWII element can be in an open or closed conformation in the individual states of the ATPase cycle [8]. The two conformations are in a dynamic equilibrium, which is controlled by the bound nucleotide. The open state is dominant in the pre-and postpower-stroke states, such as the apo-enzyme or S1 with bound ATP or ADP, or in the nucleotide states mimicked by b-c-imidoadenosine 5¢-triphosphate or ATPcS [8]. The closed conformation was attributed to the transition state and was observed with bound ADP.P i analogues, ADP.V i or ADP.AlF -4 . In the ADP.BeF x bound motor domain, both the open and closed conformation could be detected [5,7]. During the open-to-closed transition, the SWII element moves towards the c-phosphate [8]. This transition step can be followed by the hydrolysis of ATP and the closure of the active site through the relative rotation of the 50 kDa upper domain and the 50 kDa lower domain. The helix consisting of residues 648-666 is in the fulcrum of this rotation. In conjunction with this transition, the converter domain rotates by 60°, which induces the movement of the C-terminal end of S1 by 12 nm [9].Tryptophan fluorescence has proved to be a powerful experimental tool when used to characterize the different aspects of myosin interaction with nucleotides [10][11][12][13]. Rapid kinetic experiments using tryptophan fluorescence indicated Correspondence to B. Somogyi,

Facile Synthetic Procedure for ω, Primary Amine Functionalization Directly in Water for Subsequent Fluorescent Labeling and Potential Bioconjugation of RAFT-Synthesized (Co)Polymers

“…A 5 μL portion of the 0.5 M solution was then diluted with 600 μL of 20 mM phosphate/0.1 M NaCl buffer (pH 7.4). The absorbance of the polymer conjugate at 494 nm was then measured, and the concentration of 5-SFX was calculated using the reported extinction coefficient of 68 000 M -1 cm -1 . , This measurement was performed in quadruplet to ensure accuracy.…”