Heme interaction of the intrinsically disordered N-terminal peptide segment of human cystathionine-β-synthase

Abstract

Cystathionine-β-synthase (CBS) belongs to a large family of pyridoxal 5’-phosphate (PLP)-dependent enzymes, responsible for the sulfur metabolism. The heme-dependent protein CBS is part of regulatory pathways also involving the gasotransmitter hydrogen sulfide. Malfunction of CBS can lead to pathologic conditions like cancer, cardiovascular and neurodegenerative disorders. Truncation of residues 1–40, absent in X-ray structures of CBS, reduces but does not abolish the activity of the enzyme. Here we report the NMR resonance assignment and heme interaction studies for the N-terminal peptide stretch of CBS. We present NMR-spectral evidence that residues 1–40 constitute an intrinsically disordered region in CBS and interact with heme via a cysteine-proline based motif.

Hydrogen Sulfide Biochemistry and Interplay with Other Gaseous Mediators in Mammalian Physiology

“…After initial submission of this review, a quite interesting observation has been reported, which will once again stir the field of CBS heme regulation. Kumar et al observed that the N-terminal residues 1–40, so far absent from all CBS crystallographic structures, constitute an intrinsically disordered region that is able to bind heme with Cys and His as axial ligands, in a cysteine-proline-based motif [ 189 ]. This observation, deserving further exploration, constitutes an additional level of complexity regarding all the literature on the CBS heme regulation (see below).…”

Unravelling the debate on heme effects in COVID-19 infections

“…Especially in TMPRSS2, the location of the most suitable HBMs correlates with the important catalytic protease domain. This potential heme interaction would be of a transient nature, as has been observed for other heme-binding proteins such as IL-36α and CBS (Kumar et al, 2018;Wißbrock et al, 2019). Intact heme would bind to the protein surface in a reversible fashion, which would be in contrast to the recently presented hypothesis by Liu & Li (Liu and Li, 2020).…”

Assessing computational predictions of the phenotypic effect of cystathionine‐beta‐synthase variants

“…Interestingly, the functional impact of these variants was not easy to assess from sequence and structure comparisons. Although p.H65 and the sequence flanking it are locally conserved, the heme‐binding domain itself (comprising approximately the first 70 N‐terminal residues), with the exception of a short 5‐residue helix, has no secondary structure elements and does not resemble other heme proteins in either primary sequence or tertiary structure (Kumar et al, ). p.F385Q is located in the H17–H18 loop that forms part of the linker connecting the N‐terminal catalytic domain with the C‐terminal regulatory domain, and lies within an aromatic cluster of residues p.Y381, p.F332, p.F334, p.F385, p.W390, and p.F396 enclosed by salt bridges p.R336‐D388, p.K394‐E302, and p.K384‐E302 connecting helices H12–H14, H17, and H18.…”

“…Interestingly, the functional impact of these variants was not easy to assess from sequence and structure comparisons. Although p.H65 and the sequence flanking it are locally conserved, the heme-binding domain itself (comprising approximately the first 70 N-terminal residues), with the exception of a short 5-residue helix, has no secondary structure elements and does not resemble other heme proteins in either primary sequence or tertiary structure (Kumar et al, 2018). p. The hardest to predict benign variants (low pyridoxine) were surprising in that they involved nonconserved substitutions, so they could be expected to disrupt CBS function.…”