The structure of Macrophage Expressed Gene-1, a phagolysosome immune effector that is activated upon acidification

Abstract

Macrophage Expressed Gene-1 (MPEG-1; also termed Perforin-2) is an endosomal / phagolysosomal perforin-like protein that is conserved across the metazoan kingdom and that functions within the phagolysosome to damage engulfed microbes. Like the Membrane Attack Complex and perforin, MPEG-1 has been postulated to form pores in target membranes, however, its mode of action remains to be established. We used single particle cryo-Electron Microscopy to determine the 2.4 Å structure of a hexadecameric assembly of MPEG-1 that displays the expected features of a soluble pre-pore complex. We further discovered that the MPEG-1 pre-pore-like assemblies can be induced to perforate membranes through mild acidification, such as would occur within maturing phagolysosomes. We next solved the 3.6 Å cryo-EM structure of MPEG-1 in complex with liposomes. Remarkably these data revealed that a C-terminal Multi-vesicular body of 12 kDa (MVB12)-associatedβ-prism (MABP) domain interacts with target membranes in a mode that positions the pore forming machinery of MPEG-1 to point away from the bound membrane. This unexpected mechanism of membrane interaction raises the intriguing possibility that MPEG-1 may be able to remain bound to the phagolysosome membrane while simultaneously forming pores in engulfed bacterial targets.

A genome-wide survey of cnidarian Gcm-dependent genes suggests a neuronal origin of glial function

“…This suggests that N. vectensis Gcm-expressing cells are metabolically active in ways resembling astrocytes and Drosophila glia, which store energy in the form of glycogen and lipid droplets for subsequent nutrient supply to neurons 47,48,49,50 . On the other hand, an increased expression of in ammatory markers in NvGcm KD animals, a phospholypase PLA 2 51 and an immune effector, Mpeg1 52,53 , may indicate unknown involvement in the anti-in ammatory function of NvGcm. This is consistent with the recent nding of a conserved anti-in ammatory transcriptional cascade of Gcm from Drosophila to vertebrates 54 .…”

Analysis of cnidarian Gcm suggests a neuronal origin of glial EAAT1 function

“…This suggests that N. vectensis Gcm -expressing cells are metabolically active in ways resembling astrocytes and Drosophila glia, which store energy in the form of glycogen and lipid droplets for subsequent nutrient supply to neurons 47 – 50 . On the other hand, an increased expression of inflammatory marker homologs in NvGcm KD animals, a phospholypase PLA 2 51 and an immune effector, Mpeg1 52 , 53 , may indicate unknown involvement in the anti-inflammatory function of NvGcm . This is consistent with the recent finding of a conserved anti-inflammatory transcriptional cascade of Gcm from Drosophila to vertebrates 54 .…”

Oligomeric Cucurbituril Complexes: from Peculiar Assemblies to Emerging Applications

“…The hemoglobin tetramer is an archetype of such a protein oligomer, by which aggregation has enabled to improve oxygen transport [4, 5] . Helicases are circular protein oligomers, unwinding DNA strands during cell replication cycles [6] and pore‐forming proteins (such as T lymphocyte perforin) [7] circularly assemble to form pores on target cell membranes [8] . When two or more different proteins aggregate, hetero‐oligomers of precise shape can form, such as nicotinic acetylcholine receptors arranged to form ionic channels [9, 10] .…”