Biology subjects

Oliveira, C. L. P.

Publications and source records attributed to Oliveira, C. L. P..

4 recordsLinked to original sources

bioRxiv2026

Structural divergence in N-terminal domains of AAA proteases paraplegin (SPG7) and FtsH indicates a key structural function in complex formation

AAA proteases are hexameric ATP-dependent metallopeptidases that perform crucial proteolytic activities within prokaryotic and eukaryotic membranes. Structurally, protomers are comprised of catalytically active C-terminal domains that are anchored to the membrane by an N-terminal autonomous folding unit. In this study, we determined the fold, stability, and oligomeric state of the N-terminal intermembrane domains of human spastic paraplegia type 7 (SPG7)/ paraplegin protein and its bacterial orthologue FtsH using circular dichroism (CD), small-angle X-ray scattering (SAXS), small-angle neutron scattering (SANS) and X-ray crystallography. Solution-state analysis revealed that the N-terminal domain of paraplegin is a monomer in solution whereas FtsH forms a dimer. Unexpectedly, the N-terminal domain of paraplegin presents as a domain-swapped homodimer in our crystal structure that involves the first helix and first two beta-strands from one monomer and beta-strand 3, helix 2 and beta-strand 4 from another symmetry-related molecule. However, together they form an assembly which is similar to protomers observed for the N-terminal regions of FtsH and AfG3L2. Drawing from our structural data, we postulate that domain-swapping interactions of the N-terminal regions contribute to stability of the AAA protease hexamer containing paraplegin, demonstrating the extensive flexibility of the N-terminal portion of this protein and its role in achieving the appropriate molecular architecture required for function. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=87 SRC="FIGDIR/small/720153v1_ufig1.gif" ALT="Figure 1"> View larger version (26K): org.highwire.dtl.DTLVardef@1f4b9b5org.highwire.dtl.DTLVardef@1cc2242org.highwire.dtl.DTLVardef@dd211borg.highwire.dtl.DTLVardef@1a87722_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIFtsH-IMS forms a homo-dimer in solution, whereas paraplegin-IMS presents as a well-folded monomer in solution C_LIO_LIparaplegin-IMS crystallises as a domain-swapped homo-dimer but its domain-swapped monomers are structurally similar to other IMS-regions C_LIO_LIAfG3L2/paraplegin hexamer formation may be supported by domain swapping in paraplegin-IMS C_LIO_LIdomain-swapping in paraplegin could be a Bonafide feature under certain cellular conditions and may be related to disease in spastic paraplegia C_LI

biochemistry↗

bioRxiv2020

Molecular insights on CALX-CBD12 inter-domain dynamics from MD simulations, RDCs and SAXS

Na+/Ca2+ exchangers (NCX) are secondary active transporters that couple the translocation of Na+ with the transport of Ca2+ in the opposite direction. The exchanger is an essential Ca2+ extrusion mechanism in excitable cells. It consists of a transmembrane domain and a large intracellular loop that contains two Ca2+-binding domains, CBD1 and CBD2. The two CBDs are adjacent to each other and form a two-domain Ca2+-sensor called CBD12. Binding of intracellular Ca2+ to CBD12 activates the NCX but inhibits the Na+/Ca2+ exchanger of Drosophila, CALX. NMR spectroscopy and SAXS studies showed that CALX and NCX CBD12 constructs display significant inter-domain flexibility in the Apo state, but assume rigid inter-domain arrangements in the Ca2+-bound state. However, detailed structure information on CBD12 in the Apo state is missing. Structural characterization of proteins formed by two or more domains connected by flexible linkers is notoriously challenging and requires the combination of orthogonal information from multiple sources. As an attempt to characterize the conformational ensemble of CALX-CBD12 in the Apo state, we applied molecular dynamics (MD) simulations, NMR (1H-15N RDCs) and Small-Angle X-Ray Scattering (SAXS) data in a combined modelling strategy that generated atomistic information on the most representative conformations. This joint approach demonstrated that CALX-CBD12 preferentially samples closed conformations, while the wide-open inter-domain arrangement characteristic of the Ca2+-bound state is less frequently sampled. These results are consistent with the view that Ca2+ binding shifts the CBD12 conformational ensemble towards extended conformers, which could be a key step in the Na+/Ca2+ exchangers allosteric regulation mechanism. The present strategy, combining MD with NMR and SAXS, provides a powerful approach to select representative structures from ensembles of conformations, which could be applied to other flexible multi-domain systems. SIGNIFICANCEThe conformational ensemble of CALX-CBD12, the main Ca2+-sensor of Drosophilas Na+/Ca2+ exchanger, was characterized by a combination of MD simulations with SAXS and NMR data using the EOM approach. This analysis showed that this two-domain construct experiences opening-closing motions, providing molecular information about CALX-CBD12 in the Apo state. Ca2+-binding shifts the conformational ensemble towards extended conformers. These findings are consistent with a model according to which Ca2+ modulation of CBD12 plasticity is a key step in the Ca2+-regulation mechanism of the full-length exchanger.

biophysics↗

bioRxiv2020

Structural and functional analysis of pyocin S8 from Pseudomonas aeruginosa : requirement of a glutamate in the H-N-H motif for the DNase activity.

Multi-drug resistance (MDR) is a serious threat to global public health, making the development of new antimicrobials an urgent necessity. Pyocins are protein antibiotics produced by Pseudomonas aeruginosa strains to kill closely related cells during intraspecific competition. Here, we report an in depth biochemical, microbicidal and structural characterization of a new S-type pyocin, named S8. Initially, we described the domain organization and secondary structure of S8. Subsequently, we observed that a recombinant S8 composed of the killing subunit in complex with the immunity (Im) protein killed the strain PAO1. Furthermore, mutation of a highly conserved glutamic acid to alanine (Glu100Ala) completely inhibited this antimicrobial activity. Probably the integrity of the H-N-H motif is essential in the killing activity of S8, as Glu100 is a highly conserved component of this structure. Next, we observed that S8 is a metal-dependent endonuclease, as EDTA treatment abolished its ability to cleave supercoiled pUC18 plasmid. Supplementation of apo S8 with Ni2+ strongly induced this DNase activity, whereas Mn2+ and Mg2+ exhibited moderate effects and Zn2+ was inhibitory. Additionally, S8 bound Zn2+ with a higher affinity than Ni2+ and the Glu100Ala mutation decreased the affinity of S8 for these metals as shown by isothermal titration calorimetry (ITC). Finally, we describe the crystal structure of the Glu100Ala pyocin-S8DNase-Im complex at 1.38 [A], which gave us new insights into the endonuclease activity of S8. Our results reinforce the possible use of S8 as an alternative antibiotic for MDR Pseudomonas aeruginosa strains, while leaving commensal human microbiota intact.

molecular biology↗

bioRxiv2019

CALX-CBD1 Ca2+-binding cooperativity studied by NMR spectroscopy and ITC with Bayesian statistics

The Na+/Ca2+ exchanger of Drosophila melanogaster, CALX, is the main Ca2+-extrusion mechanism in olfactory sensory neurons and photoreceptor cells. Na+/Ca2+ exchangers have two Ca2+ sensor domains, CBD1 and CBD2. In contrast to the mammalian homologues, CALX is inhibited by Ca2+-binding to CALX-CBD1, while CALX-CBD2 does not bind Ca2+ at physiological concentrations. CALX-CBD1 consists of a {beta}-sandwich and displays four Ca2+ binding sites at the tip of the domain. In this study, we used NMR spectroscopy and isothermal titration calorimetry (ITC) to investigate the cooperativity of Ca2+-binding to CALX-CBD1. We observed that this domain binds Ca2+ in the slow exchange regime at the NMR chemical shift time scale. Ca2+-binding restricts the dynamics in the Ca2+-binding region. Experiments of 15N CEST and 15N R2 dispersion allowed the determination of Ca2+ dissociation rates ({approx} 20 s-1). NMR titration curves of residues in the Ca2+-binding region were sigmoidal due to the contribution of chemical exchange to transverse magnetization relaxation rates, R2. Hence, a novel approach to analyze NMR titration curves was proposed. Ca2+-binding cooperativity was examined assuming two different stoichiometric binding models and using a Bayesian approach for data analysis. Fittings of NMR and ITC binding curves to the Hill model yielded nHill = 2.9 - 3.1, near maximum cooperativity (nHill = 4). By assuming a stepwise model to interpret the ITC data, we found that the probability of binding from 2 up to 4 Ca2+ is at least three orders of magnitude higher than that of binding a single Ca2+. Hence, four Ca2+ ions bind almost simultaneously to CALX-CBD1. Cooperative Ca2+-binding is key to enable this exchanger to efficiently respond to changes in the intracellular Ca2+-concentration in sensory neuronal cells.\n\nSIGNIFICANCECALX-CBD1 is the Ca2+-sensor domain of the Na+/Ca2+ exchanger of Drosophila melanogaster. It consists of a {beta}-sandwich, and contains four Ca2+ binding sites at the distal loops. In this study, we examined the cooperative binding of four Ca2+ ions to CALX-CBD1 using NMR spectroscopy and isothermal titration calorimetry (ITC) experiments. NMR and ITC data were analyzed using the framework of the binding polynomial formalism and Bayesian statistics. A novel approach to analyze NMR titration data in the slow exchange regime was proposed. These results support the view that CALX-CBD1 binds four Ca2+ with high cooperativity. The significant ligand binding cooperativity exhibited by this domain is determinant for the efficient allosteric regulation of this exchanger by intracellular Ca2+.

biophysics↗