MONOVALENT CATION BINDING TO CUBIC INSULIN CRYSTALS

被引:40
作者
GURSKY, O
LI, YL
BADGER, J
CASPAR, DLD
机构
[1] Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, Massachusetts
关键词
D O I
10.1016/S0006-3495(92)81865-9
中图分类号
Q6 [生物物理学];
学科分类号
071011 ;
摘要
Two localized monovalent cation binding sites have been identified in cubic insulin from 2.8 angstrom-resolution difference electron density maps comparing crystals in which the Na+ ions have been replaced by Tl+. One cation is buried in a closed cavity between insulin dimers and is stabilized by interaction with protein carbonyl dipoles in two juxtaposed alternate positions related by the crystal dyad, The second cation binding site, which also involves ligation with carbonyl dipoles, is competitively occupied by one position of two alternate His B10 side chain conformations. The cation occupancy in both sites depends on the net charge on the protein which was varied by equilibrating crystals in the pH range 7-10. Detailed structures of the cation binding sites were inferred from the refined 2-angstrom resolution map of the sodium-insulin crystal at pH 9. At pH 9, the localized monovalent cations account for less than one of the three to four positive counterion charges necessary to neutralize the negative charge on each protein molecule. The majority of the monovalent counterions are too mobile to show up in the electron density maps calculated using data only at resolution higher than 10 angstrom. Monovalent cations of ionic radius < 1.5 angstrom are required for crystal stability. Replacing Na+ with Cs+, Mg++, Ca++ or La+++ disrupts the lattice order, but crystals at pH 9 with 0.1 M Li+, K+, NH4+, Rb+ or Tl+ diffract to at least 2.8 angstrom resolution.
引用
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页码:604 / 611
页数:8
相关论文
共 14 条
[1]   WATER-STRUCTURE IN CUBIC INSULIN CRYSTALS [J].
BADGER, J ;
CASPAR, DLD .
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 1991, 88 (02) :622-626
[2]   STRUCTURE OF THE PIG INSULIN DIMER IN THE CUBIC-CRYSTAL [J].
BADGER, J ;
HARRIS, MR ;
REYNOLDS, CD ;
EVANS, AC ;
DODSON, EJ ;
DODSON, GG ;
NORTH, ACT .
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE, 1991, 47 :127-136
[3]  
BAKER EN, 1988, PHILOS T R SOC LON B, V319, P365
[4]   A LEAST-SQUARES REFINEMENT METHOD FOR ISOMORPHOUS REPLACEMENT [J].
DICKERSO.RE ;
WEINZIER.JE ;
PALMER, RA .
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL CRYSTALLOGRAPHY AND CRYSTAL CHEMISTRY, 1968, B 24 :997-&
[5]   ZINC-FREE CUBIC PIG INSULIN - CRYSTALLIZATION AND STRUCTURE DETERMINATION [J].
DODSON, EJ ;
DODSON, GG ;
LEWITOVA, A ;
SABESAN, M .
JOURNAL OF MOLECULAR BIOLOGY, 1978, 125 (03) :387-396
[6]  
EISENMAN G, 1987, ANNU REV BIOPHYS BIO, V16, P205
[8]  
KALATA K, 1990, P SOC PHOTO-OPT INS, V1345, P270
[9]  
KALATA K, 1985, METHOD ENZYMOL, V114, P486
[10]  
PFLUGRATH JW, 1987, 1987 P DAR STUD WEEK