PMID:7592474

Identification and nucleotide sequences of mxaA, mxaC, mxaK, mxaL, and mxaD genes from Methylobacterium extorquens AM1

mxaA, mxaK, and mxaL are involved in incorporation of calcium into methanol dehydrogenase

"three genes (mxaAKL) involved in incorporation of calcium into methanol dehydrogenase"
Sequence analysis and mutant studies identified mxaK among other mxa genes

"A combination of sequence analysis, mutant complementation data, and gene expression studies showed that these genes correspond to mxaSACKLDorf1"

file:METEA/mxaK/mxaK-deep-research-falcon.md

Falcon deep research report: mxaK (C5AQA1) in Methylorubrum extorquens AM1

MxaK is an mxa-cluster accessory gene required for Ca2+ insertion into the MxaF active site during maturation of the Ca-dependent methanol dehydrogenase.

"required for **Ca2+ insertion into the MxaF active site**"
Deletion of mxaK yields MDH that retains MxaF/MxaI subunits but has no detectable enzymatic activity, indicating a maturation role rather than structural assembly.

"deletion of **mxaK** produced methanol dehydrogenase containing the MxaF/MxaI subunits but with **no detectable enzymatic activity**"
Activity of the inactive MDH from the mxaK deletion was restored by incubation with 10 mM CaCl2 at pH 9.5, supporting a role in Ca2+ incorporation.

"activity was restored by incubation with 10 mM CaCl2 at pH 9.5"
A mechanistic model places MxaK with MxaA, MxaC, MxaL, MxaR and MxaS acting after PQQ loading to insert Ca2+ into the MxaF catalytic center.

"MxaK functions with a set of auxiliary proteins (MxaR, MxaS, MxaA, MxaC, MxaL) in a step that occurs **after PQQ loading**"
Genome-based annotation of the AM1 mxa cluster lists mxaK among genes essential for Ca2+ insertion into MDH.

"essential for Ca2+ insertion into MDH"
Comparative genomics describes mxaK as involved in Ca2+ insertion into MxaF across Methylobacterium/Methylorubrum species.

"involved in Ca2+ insertion into MxaF"
The subcellular localization of MxaK is not directly stated in the retrieved sources and should be treated as unresolved.

"do not directly state the subcellular localization of MxaK"
No enzymatic reaction is attributed to MxaK; the evidence supports a non-catalytic maturation/assembly role.

"No direct evidence in the retrieved texts specifies whether MxaK binds Ca2+ directly, acts as a scaffold, or regulates Ca2+ transport"