Effect of N-Terminal Truncation and Solution Conditions on Chemokine Dimer Stability: Nuclear Magnetic Resonance Structural Analysis of Macrophage Inflammatory Protein 1
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- 作者：Jennifer S. Laurence ; Andy C. LiWang ; and Patricia J. LiWang
- 刊名：Biochemistry
- 出版年：1998
- 出版时间：June 30, 1998
- 年：1998
- 卷：37
- 期：26
- 页码：9346 - 9354
- 全文大小：132K
- 年卷期：v.37,no.26(June 30, 1998)
- ISSN：1520-4995
文摘
Chemokines (chemotactic cytokines) are a family ofimmune system proteins, several of whichhave been shown to block human immunodeficiency virus (HIV) infectionin various cell types. Whilethe solved structures of most chemokines reveal protein dimers,evidence has accumulated for the biologicalactivity of individual chemokine monomers, and a debate has arisenregarding the biological role of thechemokine dimer. Concurrent with this debate, several N-terminaltruncations and modifications in theCC subfamily of chemokines have been shown to have functionalsignificance, in many cases antagonizingtheir respective receptors and in some cases retaining the ability toblock HIV entry to the cell. As thedimer interface of CC chemokines is located at their N-terminus, astructural study of N-terminally truncatedchemokines will address the effect that this type of mutation has onthe dimer-monomer equilibrium.We have studied the structural consequences of N-terminaltruncation in macrophage inflammatory protein1
mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle"> (MIP-1mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">), a CC chemokine that has been shown to block HIVinfection. Examination of nuclearmagnetic resonance (NMR) spectra of a series of N-terminally truncatedMIP-1mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle"> variants reveals thatthese proteins possess a range of ability to dimerize. A mutantbeginning at amino acid Asp6 [termedMIP(6)] has near wild-type dimer properties, while furthertruncation results in weakened dimer affinity.The mutant MIP(9) (beginning with amino acid Thr9) has beenfound to exist solely as a folded monomer.Relaxation measurements yield a rotational correlation time of 8.6± 0.1 ns for wild-type MIP-1mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle"> and4.5 ± 0.1 ns for the MIP(9) mutant, consistent with a wild-typedimer and a fully monomeric MIP(9)variant. The presence of physiological salt concentrationdrastically changes the monomer-dimerequilibrium for both wild-type and most mutant proteins, heavilyfavoring the dimeric form of the protein.These results have implications for structure-function analysisof existing chemokine mutants as well asfor the larger debate regarding the biological existence and activityof the chemokine dimer.