Fitting the Pieces of the β-barrel Assembly Machinery Complex

Abstract

β-barrel membrane proteins are found in the outer membranes of mitochondria, chloroplasts, and Gram-negative bacteria; however, exactly how they are folded and inserted remains unknown. Over the past decade, both functional and structural studies have greatly contributed to addressing this elusive mechanism. It is known that a conserved core machinery is required for each organelle, though, the overall composition varies significantly. The vast majority of studies to understand the biogenesis of β-barrel membrane proteins has been done in Gram-negative bacteria. Here, it is the task of a multi-component complex known as the β-barrel assembly machinery (BAM) complex to fold and insert new β-barrel membrane proteins into the outer membrane. In this review, we will discuss recent discoveries with the goal of utilizing all reported structural and functional studies to piece together a current structural model for the fully assembled BAM complex.