Chemokine cysteines

In our experience with a number of chemokines, cysteine/cystine provides optimal refolding kinetics, higher yields, and lower reagent cost than the alternatives. 

T-cells, representing the adaptive arm of the immune response, also play a critical role in atherogenesis, and enter lesions in response to the chemokines inducible protein-10 (DP-10), monokine induced by DFN-y (MIG), and DFN-inducible T-cell a-chemoattractant (I-TAC), which bind CXCR3 (a chemokine receptor containing two cysteine residues separated by one amino acid), highly expressed by T lymphocytes in the plaque. The... 

Cysteine-cysteine chemokine receptor 5 (CCR5) A 32-bp deletion with a population frequency of about 0.1 in Caucasians results in truncated nonfunctional receptor. Carriers of this variant are partially protected from HIV infection, particularly the homozygous carriers. 

Details regarding structural/functional differences among chemokines and their receptors are discussed elsewhere in this volume. Briefly, chemokines (and their cognate receptors) consist of four main classes (CC, CXC, CX3C and C) based on the number and spacing of at least four conserved cysteine residues (Murphy 2002). 

The organization of chemokine families based on the cysteine sequence has functional significance. Some human chemokines can compete for binding and activation of receptors with other intrafamily chemokines. This raised the possibility that significant structural differences in chemokine-receptor interactions... 

Data from studies with other GPCRs have highlighted the importance of extracellular cysteines in ligand binding and the maintenance of the conformational integrity of the receptors. There are typically four conserved cysteine residues found on extracellular domains of chemokine receptors (see Figure 1 and Tables 2 and 3) one on the amino-terminus and one on each of the three extracellular loops. It is clear that the cysteines on extracellular loops 1 and 2 form a disulfide bond that is essential for the proper trafficking of the receptors... 

A further importance of cysteines lies in the palmitoylation of chemokine receptors. Many chemokine receptors have cysteine residues in their carboxy-terminal regions. In other GPCRs, these have been implicated in palmitoylation and in the anchoring of the carboxy-terminus to the plasma membrane. This effectively generates a fourth intracellular loop in the receptors. Studies on CCR5 have identified a three-cysteine cluster in the carboxy-terminus that is... 

Blanpain C, Lee B, Vakili J, et al. Extracellular cysteines of CCR5 are required for chemokine binding, but dispensable for HIV-1 coreceptor activity. J Biol Chem 1999 274(27) 18902-18908. 

Clustering of a certain number of CD4 and coreceptor molecules is presumed to be necessary for the efficient HIV-1 Env-mediated fusion pore formation. It has been proposed that four to six CCR5 molecules (91) and three CD4 binding events are needed to induce fusion between the viral and host cell membranes (92). Both CD4 (93) and chemokine receptors can form functional dimers (94) in the plasma membrane. It was proposed that formation of CD4 dimers, mediated by a disulfide bond between the cysteine residues of the D2 domain, might enhance HIV-1 entry and infection (95,96). In contrast, others have provided... 

The CXC chemokines can be divided into two groups on the basis of a structure/function domain consisting of the presence or absence of three amino acid residues (Glu-Leu-Arg ELR motif) that precedes the first cysteine amino acid residue in the primary structure of these cytokines. The ELR+ CXC chemokines are chemoattractants for neutrophils and act as potent angiogenic factors (6). In contrast, the ELR" CXC chemokines are chemoattractants for mononuclear cells and are potent inhibitors of angiogenesis (Table 1) (6). 

Chemokines are the largest family of cytokines. Four invariant cysteines define the chemokine proteins. They are grouped on the basis of the conservation of the domain containing the first two cysteines. 

Also termed 7-chemokines, C Chemokines are composed of only two cysteines one on the N-terminus and the other a downstream cysteine. There are two chemokines in this group, lymphotactin-a (XCL1) and lymphotactin-(3 (XCL2). Their function is the attraction of T-cell precursors to the thymus. 

Also termed 8-chemokines, CX3C Chemokines are composed of three amino acids between the two cysteines. This subgroup has only one member, fractalkine (CX3CL1). CX3C chemokines are secreted as well as present on the cell surface and serve both as a chemoattractant and as an adhesion molecule. 

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