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Monoclinic polymorph of Boc‐Trp‐Ile‐Ala‐Aib‐Ile‐Val‐Aib‐Leu‐Aib‐Pro‐OMe(anhydrous)

1988; Wiley; Volume: 31; Issue: 6 Linguagem: Inglês

10.1111/j.1399-3011.1988.tb00915.x

0367-8377

Isabella L. Karle, JUDITH L. FLIPPEN‐ANDERSON, M. Sukumar, P. Balaram,

Enzyme Structure and Function

The structures of two crystal forms of Boc‐Trp‐Ile‐Ala‐Aib‐Ile‐Val‐Aib‐Leu‐Aib‐Pro‐OMe have been determined. The triclinic form (PI, Z = l) from DMSO/H 2 O crystallizes as a dihydrate (Karle, Sukumar & Balaram (1986) Proc. Natl. Acad. Sci. USA 83, 9284‐9288). The monoclinic form (P2 1 , Z = 2) crystallized from dioxane is anhydrous. The conformation of the peptide is essentially the same in both crystal systems, but small changes in conformational angles are associated with a shift of the helix from a predominantly α‐type to a predominantly 3 10 ‐type. The r.m.s. deviation of 33 atoms in the backbone and Cβ positions of residues 2‐8 is only 0.29 Å between molecules in the two polymorphs. In both space groups, the helical molecules pack in a parallel fashion, rather than antiparallel. The only intermolecular hydrogen bonding is head‐to‐tail between helices. There are no lateral hydrogen bonds. In the P2 1 cell, a = 9.422(2)Å, b = 36.392(11)Å, c = 10.548(2)Å, β= 111.31(2)° and V = 3369.3Å 3 For 2 molecules of C 60 H 97 N 11 O 10 per cell.