This family includes distant homologs of mitochondrial carrier proteins (MCs, also known in mammals as solute carrier family 25, SLC25). Sequence analysis suggest that it is likely that Lpg1137 forms a standard MC structure with a pseudo-threefold symmetry with six transmembrane helices. Furthermore, sequence logos of the repeats in homologues of Lpg1137, compared to sequence logo of the eukaryotic mitochondrial carriers support the structural similarity by highlighting the conservation of structurally important Pro and Gly residues (e.g., Pro at positions 15 and 239 in the logos or the YxG motif at positions 45-47 [1]. It was previously thought that members of this family are serine proteases that target the mitochondria-associated ER membrane (MAM) and degrades STX17 (syntaxin 17), a SNARE implicated in macroautophagy/autophagy as well as mitochondria dynamics and membrane trafficking in fed cells [2,3].

1: The Legionella pneumophila effector Lpg1137 is a homologue of mitochondrial SLC25 carrier proteins, not of known serine proteases. Gradowski M, Pawlowski K; PeerJ. 2017;5:e3849. PMID:28966893

2: Legionella effector Lpg1137 shuts down ER-mitochondria communication through cleavage of syntaxin 17. Arasaki K, Mikami Y, Shames SR, Inoue H, Wakana Y, Tagaya M; Nat Commun. 2017;8:15406. PMID:28504273

3: Legionella blocks autophagy by cleaving STX17 (syntaxin 17). Arasaki K, Tagaya M; Autophagy. 2017; [Epub ahead of print] PMID:28933649