INTERCHAIN HYDROGEN BONDING INTERACTIONS BETWEEN FILAMENTS OF ACTIN

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ydrogen-bonding interactions are crucial to the function of many biological molecules. The vibrational modes associated with hydrogen bonds fall in the far-infrared region (150-250 cm-1). Actin is the primary component of muscle fibers. The single polypeptide unit is known as G-actin. When G-actin polymerizes to form actin filaments (i.e. muscle fibers), it is called F-actin. F-actin filaments are formed as two G actin monomers are twisted into a helix and it is thought that they are held together by a network of hydrogen-bonding interactions. Thus, a comparison of the far infrared spectra of G-Hversus F-actin provides a method for studying hydrogen-bonding interactions in proteins. We have grown films of G- and F-actin on polyethylene disks and determined their far infrared spectra. We observe 3 modes (532, 544, and 590 cm-1) in both G- and F-actin. In addition, we observe intense features in the F-actin spectrum at 181 and 254 cm-1, which are absent in the monomeric G-actin, and may be assignable to hydrogen bonding interactions in the F-actin. We plan to continue our studies on G- and F-actin by growing films under different conditions, such as in the presence of D2O and varying salt concentrations. D2O is expected to shift the frequency of hydrogen-bonding interactions and various salt conditions provide different levels of polymerization of G-actin into F-actin. In addition, the polarized nature of the infrared light will make it possible to study the orientation of the actin filaments.