5M66

Crystal structure of S-adenosyl-L-homocysteine hydrolase from Bradyrhizobium elkanii in complex with adenosine

Summary for 5M66

• Entry DOI: 10.2210/pdb5m66/pdb
• Related: 1A7A 1V8B 3CE6 3OND 3ONE 3ONF 4LVC
• Descriptor: Adenosylhomocysteinase, NICOTINAMIDE-ADENINE-DINUCLEOTIDE, ADENOSINE, ... (6 entities in total)
• Functional Keywords: sahase, hydrolase, sah, sam-dependent methylation, nitrogen fixation, symbiotic bacteria, nad, conformational transition, molecular gate, adenosine
• Biological source: Bradyrhizobium elkanii
• Total number of polymer chains: 4
• Total formula weight: 215294.18

Authors

Manszewski, T.,Jaskolski, M. (deposition date: 2016-10-24, release date: 2017-05-10, Last modification date: 2024-01-17)

Primary citation

Manszewski, T.,Szpotkowski, K.,Jaskolski, M.
Crystallographic and SAXS studies of S-adenosyl-l-homocysteine hydrolase from Bradyrhizobium elkanii.
IUCrJ, 4:271-282, 2017

PubMed Abstract: -Adenosyl-l-homocysteine hydrolase (SAHase) from the symbiotic bacterium (BeSAHase) was crystallized in four ligand complexes with (i) mixed adenosine (Ado) and cordycepin (Cord; 3'-deoxyadenosine), (ii) adenine (Ade), (iii) Ado and (iv) mixed 2'-deoxyadenosine (2'-dAdo) and Ade. The crystal structures were solved at resolutions of 1.84, 1.95, 1.95 and 1.54 Å, respectively. Only the Ade complex crystallized with a dimer in the asymmetric unit, while all of the other complexes formed a crystallographically independent tetrameric assembly. In the Ado/Cord complex, adenosine is found in three subunits while the fourth subunit has cordycepin bound in the active site. In the Ade and Ado complexes only these ligand molecules are present in the active sites. The 2'-dAdo/Ade complex has Ade bound in two subunits and 2'-dAdo bound in the other two subunits. The BeSAHase fold adopted a closed conformation in the complexes with Ado, Ade and 2'-dAdo, and a semi-open conformation when cordycepin occupied the active site. An SAHase-specific molecular gate, consisting of residues His342 and Phe343, behaves differently in the different complexes, but there is no simple correlation with the ligand type. Additional small-angle X-ray scattering (SAXS) experiments confirm the tetrameric state of the protein in solution. The main conclusions from this work are (i) that the SAHase subunit does not simply oscillate between two discrete conformational open/closed states in correlation with the absence/presence of a ligand in the active site, but can also assume an intermediate form for some ligands; (ii) that the shut/open state of the molecular gate in the access channel to the active site is not correlated in a simple way with the open/closed subunit conformation or empty/occupied status of the active site, but that a variety of states are possible even for the same ligand; (iii) that a cation (typically sodium) coordinated in an intersubunit loop rigidifies a molecular hinge and thus stabilizes the closed conformation; (iv) that BeSAHase in solution is a tetramer, consistent with the model derived from crystallography.

PubMed: 28512574
DOI: 10.1107/S2052252517002433

Experimental method

X-RAY DIFFRACTION (1.951 Å)