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Structural Studies of the Methylosinus trichosporium OB3b Soluble Methane Monooxygenase Hydroxylase and Regulatory Component Complex Reveal a Transient Substrate Tunnel.
- Source :
-
Biochemistry [Biochemistry] 2020 Aug 18; Vol. 59 (32), pp. 2946-2961. Date of Electronic Publication: 2020 Jul 30. - Publication Year :
- 2020
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Abstract
- The metalloenzyme soluble methane monooxygenase (sMMO) consists of hydroxylase (sMMOH), regulatory (MMOB), and reductase components. When sMMOH forms a complex with MMOB, the rate constants are greatly increased for the sequential access of O <subscript>2</subscript> , protons, and CH <subscript>4</subscript> to an oxygen-bridged diferrous metal cluster located in the buried active site. Here, we report high-resolution X-ray crystal structures of the diferric and diferrous states of both sMMOH and the sMMOH:MMOB complex using the components from Methylosinus trichosporium OB3b. These structures are analyzed for O <subscript>2</subscript> access routes enhanced when the complex forms. Previously reported, lower-resolution structures of the sMMOH:MMOB complex from the sMMO of Methylococcus capsulatus Bath revealed a series of cavities through sMMOH postulated to serve as the O <subscript>2</subscript> conduit. This potential role is evaluated in greater detail using the current structures. Additionally, a search for other potential O <subscript>2</subscript> conduits in the M. trichosporium OB3b sMMOH:MMOB complex revealed a narrow molecular tunnel, termed the W308-tunnel. This tunnel is sized appropriately for O <subscript>2</subscript> and traverses the sMMOH-MMOB interface before accessing the active site. The kinetics of reaction of O <subscript>2</subscript> with the diferrous sMMOH:MMOB complex in solution show that use of the MMOB V41R variant decreases the rate constant for O <subscript>2</subscript> binding >25000-fold without altering the component affinity. The location of Val41 near the entrance to the W308-tunnel is consistent with the tunnel serving as the primary route for the transfer of O <subscript>2</subscript> into the active site. Accordingly, the crystal structures show that formation of the diferrous sMMOH:MMOB complex restricts access through the chain of cavities while opening the W308-tunnel.
Details
- Language :
- English
- ISSN :
- 1520-4995
- Volume :
- 59
- Issue :
- 32
- Database :
- MEDLINE
- Journal :
- Biochemistry
- Publication Type :
- Academic Journal
- Accession number :
- 32692178
- Full Text :
- https://doi.org/10.1021/acs.biochem.0c00459