Sorting and assembly machinery

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Sorting and assembly machinery (SAM) is a protein machine in the outer mitochondrial membrane that helps insert beta barrel proteins into the membrane after they are imported.

Beta barrel proteins start by moving through the Tom40 pore, which is part of the translocase of the outer membrane (TOM). SAM then takes over to finish the insertion.

SAM is made of three parts: Sam50, Sam35, and Sam37. Sam50 sits in the membrane. Sam35 and Sam37 are on the cytosolic face and are peripheral; they are not essential for survival. Sam35 likely binds substrate proteins, while Sam37 helps release them from SAM after binding.

Chaperone proteins from the small Tim family guide beta barrel proteins from TOM to SAM. The SAM core complex (the three subunits together) inserts these proteins into the outer membrane, including Tom40 and porins.

Mdm10 is another mitochondrial membrane protein that helps maintain mitochondrial shape and distribution and can interact with SAM, possibly aiding in assembling Tom40 into TOM.