Sandbox Reserved 779: Difference between revisions
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the transport of retinol and/or fatty acids [8,50]. It binds retinol with a higher affinity than does RBP [51] and, as with RBP, specific binding of retinol to b-Lg has been observed in the small intestine of the neonatal calf [3]. The structure of RBP with retinol bound within the hydrophobic calyx has been solved [2] and retinol was successfully modelled into our previous b-Lg structure [3].b-Lg contains two tryptophans, Trp19 and Trp61, and their fluorescence is altered when retinol is bound [51].<ref>PMID:9115437</ref> | the transport of retinol and/or fatty acids [8,50]. It binds retinol with a higher affinity than does RBP [51] and, as with RBP, specific binding of retinol to b-Lg has been observed in the small intestine of the neonatal calf [3]. The structure of RBP with retinol bound within the hydrophobic calyx has been solved [2] and retinol was successfully modelled into our previous b-Lg structure [3].b-Lg contains two tryptophans, Trp19 and Trp61, and their fluorescence is altered when retinol is bound [51].<ref>PMID:9115437</ref> | ||
==Molecular mechanism of the Tanford transition== | |||
Above pH 6.5, b-lactoglobulin undergoes the so-called Tanford transition which is triggered by protonation of Glu89 exhibiting an anomalously | Above pH 6.5, b-lactoglobulin undergoes the so-called Tanford transition which is triggered by protonation of Glu89 exhibiting an anomalously | ||
high pKa value. The Tanford transition involves displacement of the loop EF (residues 85 to 90) that acts as a lid which closes the protein interior/binding site below pH 7.3 and opens it at higher pH. The Tanford transition may involve some other structural changes as well. For example, the transition is accompanied by a change in the microenvironment of Tyr428 and causes an alteration in the relative orientation of monomers in the dimer by as much as 5 degrees, which breaks a number of intersubunit hydrogen bonds. It should be noted that all transitions that take place between pH 2 and pH 9 do not cause any appreciable changes in the nativelike b-barrel conformation of b-lactoglobulin. | high pKa value. The Tanford transition involves displacement of the loop EF (residues 85 to 90) that acts as a lid which closes the protein interior/binding site below pH 7.3 and opens it at higher pH. The Tanford transition may involve some other structural changes as well. For example, the transition is accompanied by a change in the microenvironment of Tyr428 and causes an alteration in the relative orientation of monomers in the dimer by as much as 5 degrees, which breaks a number of intersubunit hydrogen bonds. It should be noted that all transitions that take place between pH 2 and pH 9 do not cause any appreciable changes in the nativelike b-barrel conformation of b-lactoglobulin. | ||
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==Implications or possible application== | ==Implications or possible application== | ||
Retinol Binding | Retinol and Palmitate Binding | ||
Ever since the fortuitous observation that beta-lactoglobulin (beta-Lg), the major whey protein in the milk of ruminants, bound retinol, the details of the binding have been controversial. beta-Lg is a lipocalin, like plasma retinol-binding protein, so that ligand association was expected to make use of the central cavity in the protein.<ref>PMID:12054801</ref> | Ever since the fortuitous observation that beta-lactoglobulin (beta-Lg), the major whey protein in the milk of ruminants, bound retinol, the details of the binding have been controversial. beta-Lg is a lipocalin, like plasma retinol-binding protein, so that ligand association was expected to make use of the central cavity in the protein.<ref>PMID:12054801</ref> | ||
A cocrystallized 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.<ref>PMID:9867826</ref> | |||
Antioxidant Nature | Antioxidant Nature | ||
