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The assembly of β‐barrel membrane proteins by BAM and SAM
Author(s) -
Lundquist Karl,
Billings Evan,
Bi Maxine,
Wellnitz James,
Noinaj Nicholas
Publication year - 2021
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/mmi.14666
Subject(s) - biology , biogenesis , bacterial outer membrane , organelle biogenesis , microbiology and biotechnology , bacteria , mitochondrion , protein targeting , membrane protein , membrane , biochemistry , genetics , gene , escherichia coli
Gram‐negative bacteria, mitochondria, and chloroplasts all possess an outer membrane populated with a host of β‐barrel outer‐membrane proteins (βOMPs). These βOMPs play crucial roles in maintaining viability of their hosts, and therefore, it is essential to understand the biogenesis of this class of membrane proteins. In recent years, significant structural and functional advancements have been made toward elucidating this process, which is mediated by the β‐barrel assembly machinery (BAM) in Gram‐negative bacteria, and by the sorting and assembly machinery (SAM) in mitochondria. Structures of both BAM and SAM have now been reported, allowing a comparison and dissection of the two machineries, with other studies reporting on functional aspects of each. Together, these new insights provide compelling support for the proposed budding mechanism, where each nascent βOMP forms a hybrid‐barrel intermediate with BAM/SAM in route to its biogenesis into the membrane. Here, we will review these recent studies and highlight their contributions toward understanding βOMP biogenesis in Gram‐negative bacteria and in mitochondria. We will also weigh the evidence supporting each of the two leading mechanistic models for how BAM/SAM function, and offer an outlook on future studies within the field.