Faculty of Applied Biological Science, Gifu University, Gifu, Japan.
PLoS One. 2012;7(11):e50480. doi: 10.1371/journal.pone.0050480. Epub 2012 Nov 27.
In the methylotrophic bacterium Methylobacterium extorquens strain AM1, MxaF, a Ca(2+)-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 La(3+)-dependent. Despite the absence of Ca(2+) in the medium strain AM1 was able to grow on methanol in the presence of La(3+). Addition of La(3+) 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 La(3+), and its N-terminal amino acid sequence corresponded to that of XoxF1. The enzyme contained La(3+) as a cofactor. The ΔmxaF mutant strain could not grow on methanol in the presence of Ca(2+), but was able to grow after supplementation with La(3+). Taken together, these results show that XoxF1 participates in methanol metabolism as a La(3+)-dependent MDH in strain AM1.
在甲基营养细菌甲基杆菌菌株 AM1 中，MxaF 是一种依赖 Ca(2+)的甲醇脱氢酶（MDH），是在甲醇上生长时催化甲醇氧化的主要酶。菌株 AM1 的基因组包含另一个 MDH 基因同源物 xoxF1，其在甲醇代谢中的功能尚不清楚。在这项工作中，我们表明 XoxF1 也作为 MDH 起作用，并且依赖于 La(3+)。尽管培养基中不含 Ca(2+)，但菌株 AM1 能够在 La(3+)存在的情况下利用甲醇生长。添加 La(3+)增加了 MDH 活性，但对 mxaF 或 xoxF1 的表达水平没有影响。我们从在 La(3+)存在下用甲醇培养的菌株 AM1 中纯化 MDH，其 N 端氨基酸序列与 XoxF1 相对应。该酶含有 La(3+)作为辅因子。ΔmxaF 突变株不能在 Ca(2+)存在下利用甲醇生长，但在添加 La(3+)后能够生长。总之，这些结果表明 XoxF1 作为依赖 La(3+)的 MDH 参与菌株 AM1 中的甲醇代谢。
