Evaluating the oligomeric state of SecYEG in preprotein translocase

AUTOR(ES)

Yahr, Timothy L.

FONTE

Oxford University Press

RESUMO

SecA insertion and deinsertion through SecYEG drive preprotein translocation at the Escherichia coli inner membrane. We present three assessments of the theory that oligomers of SecYEG might form functional translocation sites. (i) Formaldehyde cross- linking of translocase reveals cross-links between SecY, SecE and SecG, but not higher order oligomers. (ii) Cross-linking of membranes containing unmodified SecE and hemagglutinin-tagged SecE (SecEHA) reveals cross-links between SecY and SecE and between SecY and SecEHA. However, anti-HA immunoprecipitates contain neither untagged SecE nor SecY cross-linked to SecE. (iii) Membranes containing similar amounts of SecE and SecEHA were saturated with translocation intermediate (I29) and detergent solubilized. Anti-HA immunoprecipitation of I29 required SecYEHAG and SecA, yet untagged SecE was not present in this translocation complex. Likewise, anti-HA immunoprecipitates of membranes containing equal amounts of SecY and SecYHA were found to contain SecYHA but not SecY. Both immunoprecipitates contain more moles of I29 than of the untagged subunit, again suggesting that translocation intermediates are not engaged with multiple copies of SecYEG. These studies suggest that the active form of preprotein translocase is monomeric SecYEG.

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