Structural diversity of heparan sulfate binding domains in chemokines

Abstract

Heparan sulfate (HS) molecules are ubiquitous in animal tissues where they function as ligands that are dramatically involved in the regulation of the proteins they bind. Of these, chemokines are a family of small proteins with many biological functions. Their well-conserved monomeric structure can associate in various oligomeric forms especially in the presence of HS. Application of protein surface analysis and energy calculations to all known chemokine structures leads to the proposal that four different binding modes are created by the folding and oligomerization of these proteins. So, based on the present state of our knowledge, four different clusters of amino acids should be involved in the recognition process. Our results help to rationalize how unique sequences of HS specifically bind any given chemokine. The conclusions open the route for a rational design of compounds of therapeutical interest that could influence chemokine activity. C hemokines, derived from chemoattractant cytokine and now comprising more than 50 members, represent a recently identified family of small proteins (8 to 12 kDa in their monomeric form). Depending on the structure of a conserved cysteine-containing motif in the amino-terminal region of the molecule, four subgroups have been characterized and named C, CC, CXC, or CX 3 C according to the number and spacing of these cysteine residues. Based on the physiological features of these proteins, chemokines also have been classified as inflammatory (or inducible) or homeostatic (or constitutive) (1, 2).Although the chemotactic effect on leukocytes represents an important activity of the chemokines, it appears that these proteins also control a range of other functions that extend well beyond the regulation of leukocyte migration, including development, angiogenesis, neuronal patterning, hematopoiesis, viral infection, wound healing, and metastasis. The chemokine receptors, 20 of which have been identified, and through which these effects are transduced, are G protein-coupled, seven-helix transmembrane receptors (2). The observation that most chemokines bind to several different receptors and that most chemokine receptors exhibit overlapping specificity raises the question of the specificity of this system. Glycosaminoglycans (GAGs) are linear polysaccharides present on all animal cell surfaces and in the extracellular matrix, where they are usually found to be attached covalently to core proteins to form the proteoglycan family (3). Each tissue produces specific repertoires of GAGs (4), some of which are known to bind and regulate chemokine activity (5, 6). Several lines of evidence point to the importance of one particular GAG, heparan sulfate (HS), in promoting chemokine activity. First, in vitro, almost all chemokines studied to date appear to bind HS, suggesting that this represents a fundamental aspect of these proteins. Second, the finding that, in vivo, T lymphocytes secrete CC chemokine as a complex with proteoglycans indicates that this form is physiologically relevant (7)....

CCL28 Has Dual Roles in Mucosal Immunity as a Chemokine with Broad-Spectrum Antimicrobial Activity

“…Given the particularly strong and selective expression of CCL28 mRNA in certain mucosal tissues such as salivary glands, mammary glands, trachea, and large intestine (3,4), which commonly secrete low-salt fluids because of reabsorption of sodium ions by the epithelial cells expressing the epithelial sodium channel (19), one important function of CCL28 in these tissues may be that it is apically secreted as an antimicrobial protein and protects the mucosal surfaces against colonizing microbes. Chemokines are well known to bind to heparan sulfate (32), an abundant component of epithelial cell surface and extracellular matrix. This ability is considered to keep chemokines locally concentrated in the vicinity of producing cells and to form a gradient within the tissue (1).…”

Examination of MCP-1 (CCL2) partitioning and presentation during transendothelial leukocyte migration

“…2 Interaction with a low-affinity receptor, the cell surface glycosaminoglycans (GAG), is usually mediated via the C-terminus of the protein and often via a specific BBXB motif. 3,4 Chemokines display a range of affinities for the various glycosaminoglycan components of cell surface and extracellular proteoglycans, predominantly binding to the highly sulfated heparin-like species, heparan sulfate. 5 The ability to discriminate between different GAG molecules is believed to reside in paired glutamic acid residues within putative GAG-binding sites.…”

Critical Role of Dendritic Cells in T Cell Retention in the Interfollicular Region of Peyer’s Patches

“…Indeed, highly differentiated connective tissue-type mast cells, but not mucosal mast cells, express high levels of heparin (30). Heparin biosynthesis is mediated by multiple complex steps involving many enzymes such as N-deacetylase/Nsulfotransferase and exostoses-1 (31,32). Exostoses-1 is required for the formation of heparan sulfate chains that bind to CCL21 on endothelial cells (16).…”