Structure of components of an intercellular channel complex in sporulating Bacillus subtilis

TY - JOUR

T1 - Structure of components of an intercellular channel complex in sporulating Bacillus subtilis

AU - Levdikov, Vladimir

AU - Blagova, Lena

AU - McFeat, Amanda Jane

AU - Fogg, Mark James

AU - Wilson, Keith Sanderson

AU - Wilkinson, Anthony

PY - 2012/4/3

Y1 - 2012/4/3

N2 - Following asymmetric cell division during spore formation in Bacillus subtilis, a forespore expressed membrane protein SpoIIQ, interacts across an intercellular space with a mother cell-expressed membrane protein, SpoIIIAH. Their interaction can serve as a molecular "ratchet" contributing to the migration of the mother cell membrane around that of the forespore in a phagocytosis-like process termed engulfment. Upon completion of engulfment, SpoIIQ and SpoIIIAH are integral components of a recently proposed intercellular channel allowing passage from the mother cell into the forespore of factors required for late gene expression in this compartment. Here we show that the extracellular domains of SpoIIQ and SpoIIIAH form a heterodimeric complex in solution. The crystal structure of this complex reveals that SpoIIQ has a LytM-like zinc-metalloprotease fold but with an incomplete zinc coordination sphere and no metal. SpoIIIAH has an alpha-helical subdomain and a protruding beta-sheet subdomain, which mediates interactions with SpoIIQ. SpoIIIAH has sequence and structural homology to EscJ, a type III secretion system protein that forms a 24-fold symmetric ring. Superposition of the structures of SpoIIIAH and EscJ reveals that the SpoIIIAH protomer overlaps with two adjacent protomers of EscJ, allowing us to generate a dodecameric SpoIIIAH ring by using structural homology. Following this superposition, the SpoIIQ chains also form a closed dodecameric ring abutting the SpoIIIAH ring, producing an assembly surrounding a 60 A channel. The dimensions and organization of the proposed complex suggest it is a plausible model for the extracellular component of a gap junction-like intercellular channel.

AB - Following asymmetric cell division during spore formation in Bacillus subtilis, a forespore expressed membrane protein SpoIIQ, interacts across an intercellular space with a mother cell-expressed membrane protein, SpoIIIAH. Their interaction can serve as a molecular "ratchet" contributing to the migration of the mother cell membrane around that of the forespore in a phagocytosis-like process termed engulfment. Upon completion of engulfment, SpoIIQ and SpoIIIAH are integral components of a recently proposed intercellular channel allowing passage from the mother cell into the forespore of factors required for late gene expression in this compartment. Here we show that the extracellular domains of SpoIIQ and SpoIIIAH form a heterodimeric complex in solution. The crystal structure of this complex reveals that SpoIIQ has a LytM-like zinc-metalloprotease fold but with an incomplete zinc coordination sphere and no metal. SpoIIIAH has an alpha-helical subdomain and a protruding beta-sheet subdomain, which mediates interactions with SpoIIQ. SpoIIIAH has sequence and structural homology to EscJ, a type III secretion system protein that forms a 24-fold symmetric ring. Superposition of the structures of SpoIIIAH and EscJ reveals that the SpoIIIAH protomer overlaps with two adjacent protomers of EscJ, allowing us to generate a dodecameric SpoIIIAH ring by using structural homology. Following this superposition, the SpoIIQ chains also form a closed dodecameric ring abutting the SpoIIIAH ring, producing an assembly surrounding a 60 A channel. The dimensions and organization of the proposed complex suggest it is a plausible model for the extracellular component of a gap junction-like intercellular channel.

UR - http://www.scopus.com/inward/record.url?scp=84859471455&partnerID=8YFLogxK

U2 - 10.1073/pnas.1120087109

DO - 10.1073/pnas.1120087109

M3 - Article

SN - 0027-8424

VL - 109

SP - 5441

EP - 5445

JO - Proceedings of the National Academy of Sciences of the United States of America

JF - Proceedings of the National Academy of Sciences of the United States of America

IS - 14

ER -