Table 4.
Structure-function of critical motifs of tear lipocalin.
| Structural Motif | Amino Acid, Strand | Function | References |
|---|---|---|---|
| Hydrophobic patches | • W17/F99 A & G internal • I98 G external |
Stabilizes ligand binding through rigidity, conserved | Gasymov et al., 1998, 2002a,b |
| Disulfide bond | • C79 & C171 • D strand & C terminus |
Induces protein rigidity, aromatic asymmetry; modulates conformational selection, conserved | Glasgow et al., 1998b |
| N terminus segment | L4-S7 & Q12-G16 A | Cysteine protease inhibition | Van't Hof et al., 1997; Wojnar et al., 2001b |
| Titratable trigger residues | R27 (AB) | Protonation triggers loop motion regulates pH dependent ligand binding | Breustedt et al., 2009; Gasymov et al., 2010b. PDB files: 1XKI, EYC |
| Calyx entry loops | AB and GH | Critical for conformational selection of ligands, pH modulated | Gasymov et al., 2009, 2010b |
| Calyx entry loop | CD | Conformational selection, constrained by disulfide | Gasymov et al., 2004b |
| Calyx entry loop | EF (hairpin) | Ligand specificity of cavity, short length add promiscuity; large range of motion | Gasymov et al., 2001, 2004b |
| Closed end loop | FG | Possible receptor recognition site, highly conserved | Gasymov et al., 2000, 2001, 2009 |
| Cation-π | • K108-F28 H &AB • R118-W17 H &A |
Stabilization of holo-conformation, conserved | Gasymov et al., 2012a |
| Trigonal cluster | K114 H, H84 F, E34 AB | External binding site for charged residues | Gasymov et al., 2007a, 2008 |
| Mg+2 H20 cluster | E128 α | Endonuclease activity, divalent cation dependent, conserved | Yusifov et al., 2000 |
| α- helix strand | F130 α- V113&I115 H | Interaction modulates strand motion for long range residue interactions | Gasymov et al., 2013 |
Amino acids are designated with single letter and numbered residue position. β strands, loops, and α-helices are designated in bold font with single letters, two letters or α, respectively.