The protein SiaA (HtsA) is part of a heme uptake pathway in Streptococcus pyogenes. In this report, we present the heme binding of the alanine mutants of the axial histidine (H229A) and methionine (M79A) ligands, as well as a lysine (K61A) and cysteine (C58A) located near the heme propionates (based on homology modeling) and a control mutant (C47A). pH titrations gave pKa values ranging from 9.0 to 9.5, close to the value of 9.7 for WT SiaA. Resonance Raman spectra of the mutants suggested that the ferric heme environment may be distinct from the wild-type; spectra of the ferrous states were similar. The midpoint reduction potential of the K61A mutant was determined by spectroelectrochemical titration to be 61±3mV vs. SHE, similar to the wild-type protein (68±3mV). The addition of guanidine hydrochloride showed two processes for protein denaturation, consistent with heme loss from protein forms differing by the orientation of the heme in the binding pocket (the half-life for the slower process ranged from less than half a day to two days). The ease of protein unfolding was related to the strength of interaction of the residues with the heme. We hypothesize that kinetically facile but only partial unfolding, followed by a very slow approach to the completely unfolded state, may be a fundamental attribute of heme trafficking proteins. Small motions to release/transfer the heme accompanied by resistance to extensive unfolding may preserve the three dimensional form of the protein for further uptake and release.
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http://dx.doi.org/10.1016/j.jinorgbio.2015.10.016 | DOI Listing |
Cytochrome P450s (CYPs) are a superfamily of thiolate-ligated heme metalloenzymes principally responsible for the hydroxylation of unactivated C-H bonds. The lower-axial cysteine is an obligatory and universally conserved residue for the CYP enzyme class. Herein, we challenge this paradigm by systematically identifying non-canonical CYPs (ncCYPs) that do not harbor a cysteine ligand.
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January 2025
Hunan University of Chinese Medicine, Changsha, Hunan, China.
We studied the effect of acteoside on a model of human corneal epithelial cells (HCEC) injury induced by HO. HCEC were divided into 4 groups and cultured for 24 h in normal medium (intact and control groups, respectively), or in a medium containing DMSO or 160 μM acteoside (DMSO and acteoside groups, respectively). Then, HO solution was added to HCEC for 4 h, except for intact cells.
View Article and Find Full Text PDFCommun Biol
January 2025
Georgia Cancer Center, Augusta University, Augusta, GA, 30912, USA.
The transsulfuration (TSS) pathway is an alternative source of cysteine for glutathione synthesis. Little of the TSS pathway in antioxidant capacity in sickle cell disease (SCD) is known. Here, we evaluate the effects of TSS pathway activation through cystathionine beta-synthase (CBS) to attenuate reactive oxygen species (ROS) and ferroptosis stresses in SCD.
View Article and Find Full Text PDFSci Rep
January 2025
Department of Pharmacy, the First Affiliated Hospital of Xi'an Jiaotong University, NO.277 Yanta West Road, Yanta District, Xi'an, 710061, Shaanxi, People's Republic of China.
4',5,6,7-tetrahydoxyisoflavone (6-hydroxygenistein, 6-OHG) is a hydroxylated derivative of genistein with excellent antioxidant activity, but whether 6-OHG can protect hypoxia-induced damage is unclear. The objective of current study was to evaluate the protective effect and underling mechanism of 6-OHG against hypoxia-induced injury via network pharmacology and cellular experiments. 6-OHG-related and hypoxia injury-related targets were screened by public databases.
View Article and Find Full Text PDFBiochem Pharmacol
January 2025
Department of Pharmacology, Toxicology and Clinical Pharmacy, University of Braunschweig - Institute of Technology, Germany. Electronic address:
Soluble guanylyl cyclase (sGC) is a well-established pharmacological target for the treatment of acute angina pectoris, pulmonary hypertension and heart failure. Histidine 105 in the heme binding pocket of sGC is a crucial residue for heme binding and natural enzyme activation by NO. It was assumed that the heme-free sGC mutants α/βH105F and α/βH105A were valuable research tools for studying NO independent sGC activators.
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