Analysing the visible conformational substates of the FK506-binding protein FKBP12

1H, 13C, 15 N chemical shift assignments of the FKBP12 protein from the pathogenic fungi Candida auris and Candida glabrata

Multi-drug resistance is becoming an increasingly severe clinical challenge not only among pathogenic bacteria but among fungal pathogens as well. Drug design is inherently more challenging for the eukaryotic fungi due to their closer evolutionary similarity to humans. The recent rapid expansion in invasive infections throughout the world by Candida auris is of particular concern due to a substantial mortality rate, comparatively facile transmission, and an increasing level of resistance to all three of the major classes of anti-fungal drugs. One promising avenue for the development of an alternative class of anti-fungal agents currently under investigation is for drugs against the FK506-binding protein FKBP12 which, when bound to that drug, inhibits the fungal calcineurin signaling pathway with a resultant diminution in virulence. The specific challenge to this approach is that the homologous human calcineurin pathway functions in controlling the tissue immunity response, so that drug selectivity for the fungal pathway must be designed. To facilitate such efforts, we report the nearly complete backbone and sidechain resonances for the FKBP12 proteins of both Candida auris and clinically significant Candida glabrata fungi.

Quantifying protein dynamics in the ps-ns time regime by NMR relaxation

Both ¹⁵N chemical shift anisotropy (CSA) and sufficiently rapid exchange linebroadening transitions exhibit relaxation contributions that are proportional to the square of the magnetic field. Deconvoluting these contributions is further complicated by residue-dependent variations in protein amide ¹⁵N CSA values which have proven difficult to accurately measure. Exploiting recently reported improvements for the implementation of T₁ and T_1ρ experiments, field strength-dependent studies have been carried out on the B3 domain of protein G (GB3) as well as on the immunophilin FKBP12 and a H87V variant of that protein in which the major conformational exchange linebroadening transition is suppressed. By applying a zero frequency spectral density rescaling analysis to the relaxation data collected at magnetic fields from 500 to 900 MHz ¹H, differential residue-specific ¹⁵N CSA values have been obtained for GB3 which correlate with those derived from solid state and liquid crystalline NMR measurements to a level similar to the correlation among those previously reported studies. Application of this analysis protocol to FKBP12 demonstrated an efficient quantitation of both weak exchange linebroadening contributions and differential residue-specific ¹⁵N CSA values. Experimental access to such differential residue-specific ¹⁵N CSA values should significantly facilitate more accurate comparisons with molecular dynamics simulations of protein motion that occurs within the timeframe of global molecular tumbling.