Histidine vibrations

Histidine vibrations The imidazole side chain of histidine often plays an important role in protein function. Unfortunately characteristic imidazole modes are rarely seen in protein Raman spectra. An extensive discussion of imidazole modes is given by Harada and Takeuchi [12]. 

In general, the resonance Raman spectra reveal strong structural similarity of the Fe " site in Rieske proteins and in proteins containing a 4-cysteine coordinated [2Fe-2S] cluster, while additional modes are observed for vibrations involving the Fe" site and the histidine ligands. 

Biophysical characterization showed that a single HRP II protein bound 17 molecules of heme [35]. In an in vitro heme polymerization assay, HRP II promoted the synthesis of hemozoin, while controls, such as the proteins bovine serum albumin and lysozyme or the homopeptides polyhistidine, polylysine, and polyasparagine, did not. FT-IR analysis of the reaction product showed the characteristic vibrations of hemozoin. The polymerization activity had a pH maximum near 4.0, which dropped off precipitously near the pKa of histidine. The heme polymerization... 

In the local mechanical fluctuation model, the local motions of the amino acids on the proximal side of the heme are coupled to the heme through the side group of the proximal histidine. The side chain of the proximal histidine is covalently bonded to the Fe. This bond is the only covalent bond of the heme to the rest of the protein. Thus, motions of the a-helix that contains the proximal histidine are directly coupled the Fe. These motions can push and pull the Fe out of the plane of the heme. Since the CO is bound to the Fe, these motions may induce changes in the CO vibrational transition frequency causing pure dephasing. 

IR analysis confirmed the existence of peptides bound to the nanocluster surface. Vibrations attributed to the histidine side chains as well as from the amide stretches were present in the purified nanocluster spectra. Also, a loss of the N-H stretching band of histidine was noted, indicating a coordination mode for the peptide-metal nanostructures. This analysis confirmed the attachment of the HRE peptide to the surface. 

Figure 7 Experimental signal recorded for photolyzed MbCO. Fe-ligand vibrations dominate the cluster of modes observed in the 230-270 cm region. The clearly resolved frequency separation between the in-plane Fe-N, yr frequencies at 251 and 267 cm reflects the asymmetric interactions with the histidine ligand. The Fe-histidine stretching frequency appears at 234cm L Data were recorded under continuous illumination by a 15 mW helium neon laser with k = 633 nm. The temperature of a sensor mounted in the sapphire sample block was 15 K...

Martusevicius, S., Niaura, G., Talaikyte, Z., and Razumas, V. (1995) Adsorption of histidine on copper surface as evidenced by surface-enhanced Raman scattering spectroscopy. Vibrational Spectroscopy, 10, 271-280. 

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