FIGURE 1.

Backbone structure of the FK1 domain of FKBP51 and sequence alignment of homologous β₄-β₅ loop segments. The β₄-β₅ loop segment is indicated in black as is Phe-67 (PDB code 3O5Q (22)). The analogous domain of FKBP52 and the single domain proteins FKBP12 and FKBP12.6 are the evolutionarily closest FKBP domains to the FK1 domain of FKBP51 in the human genome (63). Strands β₁ to β₅ are numbered in accord with the FKBP12 alignment. Residues 119 and 124 are the only positions in the β₄-β₅ loop that differ between FKBP51 and FKBP52.