Sandbox Reserved 779: Difference between revisions
From Proteopedia
Jump to navigationJump to search
Rini Triani (talk | contribs) No edit summary |
Rini Triani (talk | contribs) No edit summary |
||
| Line 40: | Line 40: | ||
===Residues and secondary structures=== | ===Residues and secondary structures=== | ||
β-Lactoglobulin consists of 162 amino acid residues (18 kDa), containing two disulfide bonds (Cys 66–Cys 160 and Cys 106–Cys 119) and a free thiol (Cys 121). Structures of βLG have been reported by several groups with X-ray crystallography [19–21] and solution NMR [29,40,41].<ref>PMID:19362581</ref>It is a predominantly β-sheet protein. The β-barrel, or so called calyx, is conical and is made of two β-sheets: the B–D strands and N-terminal half of the A strand (denoted AN) form one sheet, and the E–H strands and C-terminal half of the A strand (denoted AC) form the other. On the outer surface of the β-barrel, between the G and H strands, is the 3-turn α-helix.The loops that connect the β-strands at the closed end of the calyx, BC, DE, and FG,are generally quite short, whereas those at the open end, AB, CD, EF,and GH, are significantly longer and more flexible. In the calyx,there is a large central cavity which is surrounded by hydrophobic residues and is accessible to solvent. This cavity provides the principal ligand-binding site. | β-Lactoglobulin consists of 162 amino acid residues (18 kDa), containing two disulfide bonds (Cys 66–Cys 160 and Cys 106–Cys 119) and a free thiol (Cys 121). Structures of βLG have been reported by several groups with X-ray crystallography [19–21] and solution NMR [29,40,41].<ref>PMID:19362581</ref>It is a predominantly β-sheet protein. The β-barrel, or so called calyx, is conical and is made of two β-sheets: the B–D strands and N-terminal half of the A strand (denoted AN) form one sheet, and the E–H strands and C-terminal half of the A strand (denoted AC) form the other. On the outer surface of the β-barrel, between the G and H strands, is the 3-turn α-helix.The loops that connect the β-strands at the closed end of the calyx, BC, DE, and FG,are generally quite short, whereas those at the open end, AB, CD, EF,and GH, are significantly longer and more flexible. In the calyx,there is a large central cavity which is surrounded by hydrophobic residues and is accessible to solvent. This cavity provides the principal ligand-binding site. | ||
===Dimer/Monomer=== | ===Dimer/Monomer=== | ||
| Line 62: | Line 57: | ||
Co-crystallized β-Lg with palmitic acid, and the refined structure (R = 0.204, R free = 0.240 for 6,888 reflections to 2.5-Å resolution) reveals that the ligand binds in the central cavity in a manner similar to the binding of retinol to the related lipocalin, serum retinol-binding protein. The carboxyl group binds to both Lys-60 and Lys-69 at the entrance to the cavity. The hydrophobic tail stretches in an almost fully extended conformation into the center of the protein.<ref>PMID:9867826</ref> | Co-crystallized β-Lg with palmitic acid, and the refined structure (R = 0.204, R free = 0.240 for 6,888 reflections to 2.5-Å resolution) reveals that the ligand binds in the central cavity in a manner similar to the binding of retinol to the related lipocalin, serum retinol-binding protein. The carboxyl group binds to both Lys-60 and Lys-69 at the entrance to the cavity. The hydrophobic tail stretches in an almost fully extended conformation into the center of the protein.<ref>PMID:9867826</ref> | ||
hydrophobic ligands and lactose ligands <ref>PMID:24255705</ref> | |||
===Active sites=== | |||
βLG contains two tryptophan residues, Trp 19 on the A strand and Trp 61 on the C strand. The former is buried in the hydrophobic core whereas the latter is exposed to the solvent in the native structure, making them useful probes for monitoring site-specific conformational changes.<ref>PMID:19362581</ref> | |||
In addition, studies on the monomer–dimer equilibrium [30,32,42,43] and the reactivity of the thiol group of Cys121 which deeply buried between the α-helix and H strand [44–48] revealed other important properties of β-LG.<ref>PMID:19362581</ref> the stability of the structure also depend so heavily upon the external loop around residue 64 or the β strand with the free thiol.<ref>PMID:9115437</ref> | |||
=='''Molecular mechanism of the Tanford transition'''== | =='''Molecular mechanism of the Tanford transition'''== | ||
