CXCR4 extracellular domains and CXCR4 mutants generated. A, two recognition sites for N-linked glycosylation, designated g1 (aa (NYT, pos. 11–13) and g2 (aa NVS, pos. 176–178) are located in the extracellular CXCR4 domains. B, by replacing the first amino acid N against Q and the third amino acid S against A a set of five CXCR4 mutants lacking g1, g2 or both glycans were generated. Amino acids: A, alanine; N, asparagine; Q, glutamine; S, serine; T, threonine; V, valine; Y, tyrosine.