Acinetobacter baumannii is a clinically important pathogen that has rapidly developed resistance to many antimicrobials. Bacterial membrane homeostasis systems, such as the maintenance of lipid asymmetry (Mla) system, are important for membrane remodelling in response to perturbation through the transfer of lipids between the inner and outer membranes. A. baumannii MlaD (AbMlaD) is a component of the Mla system that contains a novel mammalian cell entry (MCE) domain of unknown function. Bioinformatic analysis indicated that the MCE domain is composed of a 47 amino acid region not found in any MlaD orthologs. We solved the structure of AbMlaD at 2.0 Å. AbMlaD forms a typical 7-stranded beta-barrel MCE domain fold where the additional region is helical. A. baumannii with a deleted mlaD gene showed a defect in growth in the presence of SDS, suggesting a role of AbMlaD in the maintenance of the outer membrane barrier of A. baumannii. Genetic complementation of the mlaD mutant with AbMlaD lacking the additional region restored the ability of the mutant strain to grow on SDS agar, showing that the additional region is not involved in maintaining outer membrane integrity. MCE domains have been shown to have roles outside of lipid transfer. To determine if the additional region interacts with proteins outside of the Mla proteins, in-vitro pull-downs using AbMlaD and the additional region deletion mutant protein as bait were performed where interacting proteins were captured directly from total membrane protein preparations and then analysed by mass spectrometry. While proteins that differentially bind MlaD and the additional region were not identified, several proteins that interact with both AbMlaD and the additional region deletion mutant were identified. Together this work provides insight into the components of A. baumannii required for membrane homeostasis, and suggest that MlaD may have a role separate to this function.