Related Experiment Videos
Steroid ring hydroxylation patterns govern cooperativity in human bile acid binding protein
Gregory P Tochtrop1, Jamie L Bruns, Changguo Tang
1Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, 660 South Euclid Avenue, Campus Box 8231, St. Louis, Missouri 63110, USA.
Biochemistry
|October 8, 2003
Summary
Human ileal bile acid binding protein (I-BABP) binds bile salts with positive cooperativity. This binding mechanism is determined by the steroid ring hydroxylation pattern, not side-chain conjugation.
Area of Science:
- Biochemistry
- Molecular Biology
- Physiology
Background:
- Human ileal bile acid binding protein (I-BABP) is part of the intracellular lipid binding protein family.
- I-BABP plays a role in the transcellular transport and enterohepatic circulation of bile salts.
Purpose of the Study:
- To investigate the calorimetric analysis of bile salt binding to human I-BABP.
- To determine the structural features governing cooperativity in bile salt-I-BABP interactions.
Main Methods:
- Isothermal titration calorimetry was used to monitor the interaction of I-BABP with various bile salt derivatives.
- Chemical synthesis of side-chain-extended bile salt variants was performed to test specific structural hypotheses.
Main Results:
- All tested bile salts bound to I-BABP with a 2:1 stoichiometry and similar overall affinity.
- Derivatives of cholic acid showed significantly higher Hill coefficients, indicating greater positive cooperativity.
- Synthetic bile salt variants lacking specific side-chain features exhibited similar binding profiles to natural bile salts.
Conclusions:
- Cooperativity in bile salt recognition by I-BABP is primarily dictated by the hydroxylation pattern on the steroid B- and C-rings.
- The type or presence of side-chain conjugation does not significantly influence the cooperativity of bile salt binding to I-BABP.