Structural Changes in Loop 1 and Helix 1 of A234T TRβ Mutant Conformations of A234T mutant (carbon atoms in yellow) and wild-type (carbon atoms in green) regions of TRβ LBD are superimposed. Substitution of Ala 234 by a Thr residue pushes loop 1 away from the native position. The position of the main chain of Thr 234 is significantly altered compared with Ala 234 in wild type as indicated by the black arrows, thus decreasing the length of helix 1 by one residue. Red and blue atoms represent oxygen and nitrogen, respectively. The body of the receptor is represented as a molecular surface calculated with a 1.4-Å probe.