Human neutrophil lipocalin

The lipocalin superfamily of over 20 structurally related secreted proteins have heen extensively used as biochemical markers of disease. Some of the more well-known hpocahns include retinol-binding protein. Protein HC (a -microglobulin, a -m), and human neutrophil lipocahn/ neutrophil gelatinase-associated lipocalin (HNL/NGAL) [110]. 

Xu SY, Carlson M, Engstrom A, Garcia R, Peterson CG, Venge P (1994) Purification and characterization of a hitman neutrophil lipocalin (HNL) from the secondary granules of human neutrophils. Scand J Clin Lab Invest 54(5) 365-376... 

The C-terminal disulfide bond is obviously conserved in the hpocalin family, especially in those members that possess just one of them, e.g., the human neutrophil gelatinase-associated lipocalin (hNGAL) [33, 34]. Yet, there are certain local deviations as in the BBP, where this link is made to a Cys residue in strand B instead of strand D, as in RBP. Some lipocalins do not possess disulfide bonds at all, e.g., the bacterial lipocalin [20]. Hence, it seems that stabilization of the hpoca-lin architecture does not generally necessitate disulfide cross-links, contrasting with the immunoglobulin fold [35]. 

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