Structures of the human OSTα/β protein place a bile acid in a groove along the transporter’s surface. A peer-reviewed laboratory study combines microscopy, transport measurements and simulations to support movement through this lateral route. The finding details the return of absorbed bile acids toward the liver; it is a molecular mechanism rather than a tested treatment.
A human membrane protein called OSTα/β offers a lateral route for bile acids to cross the cell membrane. In a single peer-reviewed laboratory study, taurocholate, a bile acid, bound in a groove on the protein’s surface. The central cavity instead contained lipids. OSTα/β normally helps return bile acids absorbed by intestinal cells toward the liver, completing part of their recycling route.[1]
Cryo-electron microscopy, which images frozen molecular samples, resolved the unbound protein at a resolution of 2.7 angstroms, with a separate 3.2-angstrom structure for its taurocholate complex. Changes to selected protein residues and cell transport measurements tested the groove’s functional role. Both protein subunits were needed for robust transport. Some changes also affected protein abundance, complicating the interpretation of reduced transport in those cases.[1]
Transport measurements supported movement in both directions, following a concentration gradient without consuming adenosine triphosphate (ATP), an energy-carrying molecule in cells. Computer simulations also favoured movement along the lateral groove. The bound and unbound structures showed only subtle differences. These structural, cellular and computational findings support a transport mechanism; the study did not test a new medicine or treatment in patients.[1]
