Protein optical activity

I would suggest that the formation of metal chelate complexes, with a four or six-coordinate metal partly bound to an optically active protein and partly bound to a substrate molecule can explain this stereospecificity. The optically active coordination compounds of metals, such as cobalt, have extraordinarily high molecular rotation, and so the difference in chelation powers of the d and I forms of a substrate may be very great. As Dr. Chaberek has pointed out (Lecture 33), this chelation may involve both metals of constant valency, e.g.. Mg, Zn, and those of variable valency. Metallic ions of both types are proven essential trace metals in biological systems. 

The asterisk signifies an asymmetric carbon. AH of the amino acids, except glycine, have two optically active isomers designated D- or L-. Isoleucine and threonine also have centers of asymmetry at their P-carbon atoms (1,10). Protein amino acids are of the L-a-form (1,10) as illustrated in Table 1. 

Optical activity in conjugated proteins. G. Blauer, Struct. Bonding (Berlin), 1974,18, 69-129 (393). 

Blauer G (1974) Optical Activity of Conjugated Proteins. 18 69-129 Bleijenberg KC (1980) Luminescence Properties of Uranate Centres in Solids. 42 97-128 Boca R, Breza M, Pelikan P (1989) Vibronic Interactions in the Stereochemistry of Metal Complexes 71 57-97... 

Regioselective Beckmann rearrangements were used as key steps in the synthesis of phosphonoalkyl azepinones (Scheme 36) [43b] and in a formal total synthesis of the protein kinase C inhibitor balanol (Scheme 37) the optically active azide 197 derived from cyclohexadiene mono-oxide was converted into ketone 198 in several steps. After preparation of the oxime tosylates 199 (2.3 1 mixture), a Lewis acid mediated regioselective Beckmann rearrangement gave the lactams 200 and 201 in 66% and 9% yield, respectively. Lactam 201 underwent a 3-e im-ination to give additional 200, which served as a key intermediate in a balanol precursor synthesis (Scheme 37) [43 cj. 

UNFOLDED PROTEINS STUDIED BY RAMAN OPTICAL ACTIVITY... 

III. Survey of Polypeptide and Protein Raman Optical Activity. 59... 

B. Raman Optical Activity Band Assignments for Folded Proteins. 60... 

Raman optical activity is an excellent technique for studying polypeptide and protein structure in aqueous solution since, as mentioned above, their ROA spectra are often dominated by bands originating in the peptide backbone that directly reflect the solution conformation. Furthermore, the special sensitivity of ROA to dynamic aspects of structure makes it a new source of information on order-disorder transitions. 

Raman optical activity has proved valuable in recent studies of the structure and behavior of a number of natively unfolded proteins found in quite different biological situations. Although completely unfolded, the structures appear to be more stable than those generated by complete unfolding of proteins having a tertiary fold in their native states. Such natively unfolded proteins clearly have special characteristics built into their amino acid sequences that prevent aggregation under normal physiological conditions. 

---