A Catalytic Role of XoxF1 as La3+-Dependent Methanol Dehydrogenase in Methylobacterium extorquens Strain AM1

Tomoyuki Nakagawa,Akio Tani,Kentaro Sasa,Shinya Tashiro,Takashi Hayakawa,Ryoji Mitsui,Tomonori Iwama,Keiichi Kawai,John R Battista

doi:10.1371/journal.pone.0050480

Tomoyuki Nakagawa, Akio Tani + Show 7 more

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https://doi.org/10.1371/journal.pone.0050480

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Abstract

In the methylotrophic bacterium Methylobacterium extorquens strain AM1, MxaF, a Ca2+-dependent methanol dehydrogenase (MDH), is the main enzyme catalyzing methanol oxidation during growth on methanol. The genome of strain AM1 contains another MDH gene homologue, xoxF1, whose function in methanol metabolism has remained unclear. In this work, we show that XoxF1 also functions as an MDH and is La3+-dependent. Despite the absence of Ca2+ in the medium strain AM1 was able to grow on methanol in the presence of La3+. Addition of La3+ increased MDH activity but the addition had no effect on mxaF or xoxF1 expression level. We purified MDH from strain AM1 grown on methanol in the presence of La3+, and its N-terminal amino acid sequence corresponded to that of XoxF1. The enzyme contained La3+ as a cofactor. The ΔmxaF mutant strain could not grow on methanol in the presence of Ca2+, but was able to grow after supplementation with La3+. Taken together, these results show that XoxF1 participates in methanol metabolism as a La3+-dependent MDH in strain AM1.

Highlights

Methylotrophs are microorganisms with the ability to utilize reduced C1-compounds, such as methane, methanol and methylamine as their sole carbon and energy source
We showed that lanthanum (La), cerium (Ce), and praseodymium (Pr), all of which are belong to the rare earth elements (REE), increased methanol dehydrogenase (MDH) activity in cell extracts of M. radiotolerans and the non-methylotrophic bacteria Bradyrhizobium sp. [23,24]
We showed that some REEs increased MDH activity in M. radiotolerans and the non-methylotrophic Bradyrhizobium sp. [23,24]

Summary

Introduction

Methylotrophs are microorganisms with the ability to utilize reduced C1-compounds, such as methane, methanol and methylamine as their sole carbon and energy source. They are ubiquitous in nature, and some of them are well-known plant epiphytes [1,2]. In the methylotrophic metabolism of Methylobacterium, methanol is first oxidized to formaldehyde via methanol dehydrogenase (MDH) in the periplasm [13,14]. MxaF and MxaI are encoded by mxaFI genes located in the large mxa gene cluster [17], and both are essential for growth on methanol, as the loss of these genes in strain AM1 eliminates virtually all methanol dehydrogenase activity [18,19]

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