Component of the ERMES/MDM complex, which serves as a molecular tether to connect the endoplasmic reticulum (ER) and mitochondria. Components of this complex are involved in the control of mitochondrial shape and protein biogenesis, and function in nonvesicular lipid trafficking between the ER and mitochondria. Mdm34 is required for the interaction of the ER-resident membrane protein mmm1 and the outer mitochondrial membrane-resident beta-barrel protein mdm10. Component of the ER-mitochondria encounter structure (ERMES) or MDM complex, composed of mmm1, mdm10, mdm12 and mdm34. The ERMES/MDM complex localizes to a few discrete foci (around 10 per single cell), that represent mitochondria-endoplasmic reticulum junctions. These foci are often found next to mtDNA nucleoids. Lacks alpha-helical transmembrane segments, suggesting that it resides in the membrane via beta-sheet conformations similar to those predicted for other outer membrane proteins and porin. The SMP-LTD domain is a barrel-like domain that can bind various types of glycerophospholipids in its interior and mediate their transfer between two adjacent bilayers. Belongs to the MDM34 family.