Molecular interactions between multihaem cytochromes: probing the protein–protein interactions between pentahaem cytochromes of a nitrite reductase complex

2011 ◽  
Vol 39 (1) ◽  
pp. 263-268 ◽  
Author(s):  
Colin Lockwood ◽  
Julea N. Butt ◽  
Thomas A. Clarke ◽  
David J. Richardson

The cytochrome c nitrite reductase NrfA is a 53 kDa pentahaem enzyme that crystallizes as a decahaem homodimer. NrfA catalyses the reduction of NO2− to NH4+ through a six electron reduction pathway that is of major physiological significance to the anaerobic metabolism of enteric and sulfate reducing bacteria. NrfA receives electrons from the 21 kDa pentahaem NrfB donor protein. This requires that redox complexes form between the NrfA and NrfB pentahaem cytochromes. The formation of these complexes can be monitored using a range of methodologies for studying protein–protein interactions, including dynamic light scattering, gel filtration, analytical ultracentrifugation and visible spectroscopy. These methods have been used to show that oxidized NrfA exists in dynamic monomer–dimer equilibrium with a Kd (dissociation constant) of 4 μM. Significantly, the monomeric and dimeric forms of NrfA are equally active for either the six electron reduction of NO2− or HSO3−. When mixed together, NrfA and NrfB exist in equilibrium with NrfAB, which is described by a Kd of 50 nM. Thus, since NrfA and NrfB are present in micromolar concentrations in the periplasmic compartment, it is likely that NrfB remains tightly associated with its NrfA redox partner under physiological conditions.

2002 ◽  
Vol 362 (2) ◽  
pp. 317-327 ◽  
Author(s):  
Shabih-e-Hassnain SYED ◽  
Brian TRINNAMAN ◽  
Stephen MARTIN ◽  
Sarah MAJOR ◽  
Jon HUTCHINSON ◽  
...  

Desmocollins (Dscs) and desmogleins (Dsgs) are cell-adhesion molecules involved in the formation of desmosome cell—cell junctions and share structural similarities to classical cadherins such as E-cadherin. In order to identify and provide quantitative information on the types of protein—protein interactions displayed by the type 2 isoforms and investigate the role of Ca2+ in this process, we have developed an Escherichia coli expression system to generate recombinant proteins containing the first two extracellular domains, namely Dsg2(1-2) and Dsc2(1-2). Analytical ultracentrifugation, chemical cross-linking, CD, fluorescence and BIAcore have been used to provide the first direct evidence of Ca2+ binding to desmosomal cadherins. These studies suggest that Dsc2(1-2) not only exhibits homophilic interactions in solution, but can also form heterophilic interactions with Dsg2(1-2). The latter, on the other hand, shows much weaker homophilic association. Our results further demonstrate that heterophilic interactions are Ca2+-dependent, whereas the Ca2+-dependence of homophilic association is less clear. Our data indicate that the functional properties of Dsc2(1-2) are more similar to those of classical cadherins, consistent with the observation that Dsc shares a higher level of sequence homology with classical cadherins than does Dsg. In addition to corroborating the conclusions of previously reported transfection studies which suggest the formation of lateral heterodimers and homodimers, our results also provide direct quantitative information on the strength of these interactions which are essential for understanding the adhesion mechanism.


Microbiology ◽  
2003 ◽  
Vol 149 (10) ◽  
pp. 2733-2738 ◽  
Author(s):  
Susanne Rohrer ◽  
Brigitte Berger-Bächi

Protein–protein interactions play an important role in all cellular processes. The development of two-hybrid systems in yeast and bacteria allows for in vivo assessment of such interactions. Using a recently developed bacterial two-hybrid system, the interactions of the Staphylococcus aureus proteins FemA, FemB and FmhB, members of the FemABX protein family, which is involved in peptidoglycan biosynthesis and β-lactam resistance of numerous Gram-positive bacteria, were analysed. While FmhB is involved in the addition of glycine 1 of the pentaglycine interpeptide of S. aureus peptidoglycan, FemA and FemB are specific for glycines 2/3 and 4/5, respectively. FemA–FemA, FemA–FemB and FemB–FemB interactions were found, while FmhB exists solely as a monomer. Interactions detected by the bacterial two-hybrid system were confirmed using the glutathione S-transferase-pulldown assay and gel filtration.


2018 ◽  
Author(s):  
P. De-la-Torre ◽  
D. Choudhary ◽  
R. Araya-Secchi ◽  
Y. Narui ◽  
M. Sotomayor

ABSTRACTThe cadherin superfamily of proteins is defined by the presence of extracellular cadherin (EC) repeats that engage in protein-protein interactions to mediate cell-cell adhesion, cell signaling, and mechanotransduction. The extracellular domains of non-classical cadherins often have a large number of EC repeats along with other subdomains of various folds. Protocadherin-15 (PCDH15), a protein component of the inner-ear tip link filament essential for mechanotransduction, has eleven EC repeats and a membrane adjacent domain (MAD12) of atypical fold. Here we report the crystal structure of a pig PCDH15 fragment including EC10, EC11, and MAD12 in a parallel dimeric arrangement. MAD12 has a unique molecular architecture and folds as a ferredoxin-like domain similar to that found in the nucleoporin protein Nup54. Analytical ultracentrifugation experiments along with size exclusion chromatography coupled to multi-angle laser light scattering and small-angle X-ray scattering corroborate the crystallographic dimer and show that MAD12 induces parallel dimerization of PCDH15 near its membrane insertion point. In addition, steered molecular dynamics simulations suggest that MAD12 is mechanically weak and may unfold before tip-link rupture. Sequence analyses and structural modeling predict the existence of similar domains in cadherin-23, protocadherin-24, and the “giant” FAT and CELSR cadherins, indicating that some of them may also exhibit MAD-induced parallel dimerization.


Biomolecules ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 1317
Author(s):  
Sigalit Sukenik ◽  
Ilana Braunstein ◽  
Ariel Stanhill

Maintaining 26S proteasome activity under diverse physiological conditions is a fundamental requirement in order to maintain cellular proteostasis. Several quantitative and qualitative mechanisms have evolved to ensure that ubiquitin–proteasome system (UPS) substrates do not accumulate and lead to promiscuous protein–protein interactions that, in turn, lead to cellular malfunction. In this report, we demonstrate that Arsenite Inducible Regulatory Particle-Associate Protein (AIRAP), previously reported as a proteasomal adaptor required for maintaining proteasomal flux during arsenite exposure, can directly bind arsenite molecules. We further show that arsenite inhibits Psmd14/Rpn11 metalloprotease deubiquitination activity by substituting zinc binding to the MPN/JAMM domain. The proteasomal adaptor AIRAP is able to directly relieve PSMD14/Rpn11 inhibition. A possible metal relay between arsenylated PSMD14/Rpn11 and AIRAP may serve as a cellular mechanism that senses proteasomal inhibition to restore Psmd14/Rpn11 activity.


2020 ◽  
Vol 3 (1) ◽  
Author(s):  
Xiaoyi Tan ◽  
Hai Chen ◽  
Chunkai Gu ◽  
Jiachen Zang ◽  
Tuo Zhang ◽  
...  

Abstract Histidine (His) residues represent versatile motifs for designing protein-protein interactions because the protonation state of the imidazole group of His is the only moiety in protein to be significantly pH dependent under physiological conditions. Here we show that, by the designed His motifs nearby the C4 axes, ferritin nanocages arrange in crystals with a simple cubic stacking pattern. The X-ray crystal structures obtained at pH 4.0, 7.0, and 9.0 in conjunction with thermostability analyses reveal the strength of the π–π interactions between two adjacent protein nanocages can be fine-tuned by pH. By using the crystal structural information as a guide, we constructed 3D protein frameworks in solution by a combination of the relatively weak His–His interaction and Ni2+-participated metal coordination with Glu residues from two adjacent protein nanocages. These findings open up a new way of organizing protein building blocks into 3D protein crystalline frameworks.


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