Differential conformational dynamics in the closely homologous FK506-binding domains of FKBP51 and FKBP52

Abstract

As co-chaperones of Hsp90 (heat-shock protein 90), FKBP51 (FK506-binding protein of 51 kDa) and FKBP52 (FK506-binding protein of 52 kDa) act as antagonists in regulating the hormone affinity and nuclear transport of steroid receptor complexes. Exchange of Leu ¹¹⁹ in FKBP51 for Pro ¹¹⁹ in FKBP52 has been shown to largely reverse the steroid receptor activities of FKBP51 and FKBP52. To examine whether differences in conformational dynamics/plasticity might correlate with changes in the reported receptor activities, ¹⁵N-NMR relaxation measurements were carried out on the N-terminal FKBP domains of FKBP51 and FKBP52 as well as their residue-swapped variants. Both proteins exhibit a similar pattern of motion in the picosecond–nanosecond timeframe as well as a small degree of ¹⁵N line-broadening, indicative of motion in the microsecond–millisecond timeframe, in the β _3a strand of the central sheet. Only the FKBP51 domain exhibits much larger line-broadening in the adjacent β ₃ bulge (40′s loop of FKBP12) and throughout the long β ₄–β ₅ loop (80′s loop of FKBP12). The L119P mutation at the tip of the β ₄–β ₅ loop completely suppressed the line-broadening in this loop while partially suppressing the line-broadening in the neighbouring β ₂ and β _3a strands. The complementary P119L and P119L/P124S variants of FKBP52 yielded similar patterns of line-broadening for the β ₄–β ₅ loop as that for FKBP51, although only 20% and 60% as intense respectively. However, despite the close structural similarity in the packing interactions between the β ₄–β ₅ loop and the β _3a strand for FKBP51 and FKBP52, the line-broadening in the β _3a strand is unaffected by the P119L or P119L/P124S mutations in FKBP52.

Abstract

Unlike FKBP52, the FK1 domain of FKBP51 exhibits microsecond–millisecond conformational dynamics in the β ₃ bulge and the β ₄–β ₅ loop, known sites of protein signalling interactions. Swapping residue 119 yields altered conformational dynamics in a pattern reminiscent of reported modulations in steroid receptor activity.