MTX3

MTX3 is a mitochondrial protein containing a glutathione S-transferase (GST) domain that belongs to the metaxin family, sharing 40% identity with MTX1 and 26% with MTX2 (PMID:15087125). It resides in a membrane-bridging subcomplex (subcomplex B) of the mitochondrial intermembrane space bridging (MIB) complex together with SAMM50 and MTX2, distinct from the core MICOS complex (PMID:26477565). Its precise molecular function within the MIB complex is uncharacterized.

1. 2004 Medium

   Cloning and domain analysis of zebrafish mtx3 established that the metaxin family has a third member with a conserved GST domain and predominantly alpha-helical structure, defining the protein's architecture before any functional data existed.

   Evidence cDNA cloning, sequence alignment, and domain prediction in zebrafish

   PMID:15087125

   Open questions at the time

   • No functional assay performed; domain architecture alone does not demonstrate enzymatic or structural activity
   • Human MTX3 protein not directly characterized in this study
   • Whether the GST domain possesses catalytic transferase activity is untested
2. 2015 Medium

   Complexome profiling placed human MTX3 within a specific membrane-bridging subcomplex of the MIB complex alongside SAMM50 and MTX2, establishing its physical context in mitochondrial architecture.

   Evidence Native gel electrophoresis coupled to mass spectrometry fractionation of mitochondrial protein complexes

   PMID:26477565

   Open questions at the time

   • No reciprocal co-immunoprecipitation or mutagenesis to validate direct protein–protein interactions
   • Functional consequence of MTX3 depletion on MIB complex integrity or mitochondrial morphology is unknown
   • Whether MTX3 contacts the inner membrane MICOS subunits or only outer membrane components is unresolved

• The molecular function of MTX3 — whether it acts as a structural scaffold, enzymatic component, or regulatory subunit within the MIB complex — remains entirely uncharacterized.
• No loss-of-function or gain-of-function studies exist for MTX3 in any organism
• No substrate or binding partner beyond complex co-migration has been identified
• Role of the GST domain (catalytic vs. structural) is untested