J. Am. Chem. Soc. 1999, 121, 8409-8410
A Chemical Model of a Protein â-Sheet Dimer
8409
James S. Nowick,* James H. Tsai, Quoc-Chuong D. Bui, and
Santanu Maitra
Department of Chemistry, UniVersity of California, IrVine,
IrVine, California 92697-2025
ReceiVed June 21, 1999
â-Sheet formation is an important form of protein interaction
that is involved in protein dimerization, recognition between
different proteins, and protein aggregation.1 Proteins that function
as â-sheet dimers (or higher oligomers) include HIV-1 protease,
many lectins, and the defensins (Figure 1). An attractive approach
to modulating the function of these protein â-sheet dimers
involves developing synthetic molecules that can mimic or
interrupt â-sheet dimer formation.2 This paper reports our first
efforts directed toward this goal: a chemical model of a protein
â-sheet dimer.
Figure 1. Ribbon diagram of defensin HNP-3.3 (PDB reference 1dfn).4
We have previously developed monomeric chemical models
of protein â-sheets (artificial â-sheets) in which molecular
templates induce â-sheet structure in attached peptide strands.3-5
These templates include an oligourea molecular scaffold, designed
to hold multiple peptide or peptidomimetic strands in proximity,
and a 5-amino-2-methoxybenzoic acid â-strand mimic, designed
to duplicate the hydrogen-bonding functionality of one edge of a
peptide â-strand. In the present study, we combine a peptide
strand, a diurea template, and the â-strand mimic with a new
group, an oxalamide linker, to form artificial â-sheets 1. In
oxamoyl chloride adduct with amine 48 then afforded artificial
â-sheet 1a in 48-56% yield. Artificial â-sheet 1b, which contains
p-nitrophenylalanine, valine, and methionine, in place of phenyl-
alanine, isoleucine, and leucine, was prepared in a similar fashion
and with comparable yields.
1H NMR transverse-ROESY (Tr-ROESY)9 studies show that
1a adopts an intramolecularly hydrogen-bonded â-sheet structure
in CDCl3 solution (10 mM, 30 °C). Notably, 1a exhibits
interstrand ROEs between H6 of the â-strand mimic and the
isoleucine R-proton and side-chain protons. Additional interstrand
ROEs occur between the terminal methylamide and isobutryryl
groups, the leucine side-chain and isobutyryl group, the oxalamide
and urea NH groups, and the leucine and hydrazide NH groups.
Of particular significance is an ROE between the phenylalanine
and leucine R-protons. This ROE is not consistent with a
monomeric â-sheet structure and suggests the formation of an
antiparallel â-sheet dimer. Figure 2 shows the structure of this
dimer and illustrates all of these interstrand ROEs. Figure 3
provides a molecular model of this structure that is consistent
with these ROEs.
To confirm that the ROEs between the phenylalanine and
leucine R-protons of 1a are intermolecular and result from dimer
formation, we performed a crossover experiment consisting of
Tr-ROESY studies of a mixture of 1a and 1b. These studies reveal
intersheet ROEs between the phenylalanine R-proton of 1a and
the methionine R-proton of 1b and between the leucine R-proton
contrast with our previous artificial â-sheets, the â-strand mimic
is on the bottom edge of the â-sheet. Also in contrast with our
previous compounds, artificial â-sheets 1 form dimers with well-
defined structures.
Artificial â-sheet 1a was prepared from diamine 26 as shown
in eq 1. Reaction of diamine 2 with phenyalanylisoleucylleucine
methyl ester isocyanate7 and aminolysis of the methyl ester group
of the resulting urea adduct with methylamine afforded peptide
methylamide urea adduct 3a in 77% yield. Treatment of this
compound with oxalyl chloride and reaction of the resulting
(1) Maitra, S.; Nowick, J. S. â-Sheet Interactions Between Proteins. In The
Amide Linkage: Structural Significance in Chemistry, Biochemistry, and
Materials Science; Greenberg, A., Breneman C. M., Liebman, J. F., Eds.;
Wiley: New York, 2000 (in press).
(2) Zutsi, R.; Brickner, M.; Chmielewski, J. Curr. Opin. Chem. Biol. 1998,
2, 62-66.
(3) Hill, C. P.; Yee, J.; Selsted, M. E.; Eisenberg, D. Science 1991, 251,
1481-1485.
(4) This diagram was prepared using Molscript: Kraulis, P. J. J. Appl.
Crystallogr. 1991, 24, 946-950.
(5) Nowick, J. S. Acc. Chem. Res. 1999, 32, 287-296.
(6) Nowick, J. S.; Abdi, M.; Bellamo, K. A.; Love, J. A.; Martinez, E. J.;
Noronha, G.; Smith, E. M.; Ziller, J. W. J. Am. Chem. Soc. 1995, 117, 89-
99.
(8) Holmes, D. L.; Smith, E. M.; Nowick, J. S. J. Am. Chem. Soc. 1997,
119, 7665-7669.
(9) (a) Hwang, T. L.; Shaka, A. J. J. Am. Chem. Soc. 1992, 114, 3157-
3159. (b) Hwang, T. L.; Shaka, A. J. J. Magn. Reson., Ser. B 1993, 102,
155-165.
(7) Nowick, J. S.; Holmes, D. L.; Noronha, G.; Smith, E. M.; Nguyen, T.
M.; Huang, S.-L. J. Org. Chem. 1996, 61, 3929-3934. (b) Nowick, J. S.;
Holmes, D. L.; Noronha, G.; Smith, E. M.; Nguyen, T. M.; Huang, S.-L.;
Wang, E. H. J. Org. Chem. 1998, 63, 9144.
10.1021/ja992109g CCC: $18.00 © 1999 American Chemical Society
Published on Web 08/31/1999