Exploring Human Mitochondrial NFS1 Cysteine Desulfurase Structure- Function Relationships

ARÁN MARTÍN; SEWELL E; SANTOS J; CAPECE L

San Luis

Congreso; XLVIII Reunión Anual de la Sociedad Argentina de Biofísica; 2019

Iron-sulfur cluster biosynthesis is a complex mitochondrial process that requires asupercomplex formed by five different proteins NFS1, ACP, ISD11, ISCU and FXN.Homodimerization of NFS1 is crucial for its PLP-dependent Cys desulfurase activity.Moreover, the supercomplex is an heterodecamer (two subunits of each protein). ACPISD11heterodimer stabilizes the formation of the NFS1 dimer, whereas FXN produces astrong positive modulation of the enzymatic activity by stimulating -SH group transferfrom NFS1 active site to ISCU. In this process, a very conserved loop of NFS1 plays a keyrole,presumably establishing communication between the NFS1 and ISCU active sites.We analyzed loop motions by means of molecular dynamics simulations of thesupercomplex core NFS1/ACP-ISD11, and we designed loop mutants that modulate theflexibility of this element to explore structure-dynamics-function relationships.Additionally, a double mutant of NFS1 containing a single tryptophan residue (NFS1W97)was prepared. This variant was significantly more sensitive to trypsin, suggesting anincreased flexibility. This mutation eliminates a C-terminal Trp that is presumablyimportant for inter-subunit interactions. Accordingly, NFS1W97 exhibited reducedenzymatic activity assessed by measuring [H 2S ] and [Ala].These results suggest thatthe function of the supercomplex is governed by intricate relationships betweenstructure and dynamics.