Cysteine Conformational energy

Present work. MP2/cc-pVTZ geometries from cysteine conformer set used as starting stractures. For the 58 unique minima obtained, CCSD(T )-F12b/cc-pVDZ-F12 relative energies and MP2/cc-pVTZ zero-point corrections... 

In 2008, Alonso and coworkers reported a combined experimental and computational study of the conformations of cysteine. They located 11 low lying conformers at MP4/6-311-i i-G(d,p)//MP2/6-311-l-l-G(d,p), and the five lowest energy structures are shown in Table 3.15. Using laser ablation molecular beam Fourier transform microwave spectroscopy, they identified six conformers present in the gas phase. Comparing the computed rotational constants and nuclear quadrupole coupling tensor components with the experiment, they were able to decidedly match up all six experimental conformers with computed structures. Of the five low energy conformers listed in Table 3.15, four of them were identified in the experiment. 

HiPIP from Chromatium vinosum contains three tryptophan residues (W60, W76 and W80) (Fig. 7.5). The distance between tryptophan 80 and the Fe4S4 cluster (7.5 A) and their relative orientation contribute to a high energy transfer FOrster type. Fe-S bonds covalently bind the Fe4S4 cluster to the protein matrix at cysteine residues 43.46, 63 and 77. The polypeptide chain conformation may be described as a sequence of a helical or extended conformations and hairpin turns (Carter et a. 1974). 

The presence of polar functional groups in the side chains of a-amino acids is expected to increase dramatically the number of low-energy conformers. The functional group can establish additional interactions, which do not occur in other a-amino acids previously studied, and thus may affect the conformational preferences giving rise to a rich conformational space. The conformational behavior of serine [60], cysteine [134], threonine [61], aspartic acid [135], glutamic acid [67], and asparagine [136] have been revealed using LA-MB-FTMW spectroscopy. A summary of the results is collected in Table 3. The analysis of threonine... 

Threonine (R=—CH(CH3)OH, m.p. = 256°C) [61] is related to serine as it only differs on the Cy methyl group. Figure 7 shows the seven low energy conformers detected for threonine. While form lllpb observed in serine [60] and cysteine [134] was also observed in threonine, conformer lllpc was not detected. This can be attributed to the raising of the energy of this conformer caused by steric interaction of the Cy methyl group with the -COOH group. Conformer lllo,a has been observed, in contrast to serine and cysteine, where this conformer relaxes in the supersonic... 

The action pattern and kinetics of a dextranase obtained from Penicillium funiculosum have been studied. Whereas chelated cobalt compounds did not activate the enzyme, Co + ions and cobalt species bound by the enzyme enhanced its activity, with a concomitant decrease in the activation energy and an increase in l x Km was not affected. From modifications to L-lysine, L-arginine, L-histidine, and L-cysteine residues and carboxy-groups in the enzyme, it was concluded that an L-cysteine residue located outside the active site is responsible for the activation. It appears that conformational changes induced when cobalt ions combine with this amino-acid residue make it easier for the enzyme to accept dextran and for the enzyme-substrate complex to dissociate. 

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