In vitro reconstitution of sortase-catalyzed pilus polymerization reveals structural elements involved in pilin cross-linking.Chang, C., Amer, B.R., Osipiuk, J., McConnell, S.A., Huang, I.H., Hsieh, V., Fu, J., Nguyen, H.H., Muroski, J., Flores, E., Ogorzalek Loo, R.R., Loo, J.A., Putkey, J.A., Joachimiak, A., Das, A., Clubb, R.T., Ton-That, H.
(2018) Proc Natl Acad Sci U S A 115: E5477-E5486
- PubMed: 29844180
- DOI: 10.1073/pnas.1800954115
- Structures With Same Primary Citation
- PubMed Abstract:
Covalently cross-linked pilus polymers displayed on the cell surface of Gram-positive bacteria are assembled by class C sortase enzymes. These pilus-specific transpeptidases located on the bacterial membrane catalyze a two-step protein ligation react ...
Covalently cross-linked pilus polymers displayed on the cell surface of Gram-positive bacteria are assembled by class C sortase enzymes. These pilus-specific transpeptidases located on the bacterial membrane catalyze a two-step protein ligation reaction, first cleaving the LPXTG motif of one pilin protomer to form an acyl-enzyme intermediate and then joining the terminal Thr to the nucleophilic Lys residue residing within the pilin motif of another pilin protomer. To date, the determinants of class C enzymes that uniquely enable them to construct pili remain unknown. Here, informed by high-resolution crystal structures of corynebacterial pilus-specific sortase (SrtA) and utilizing a structural variant of the enzyme (SrtA 2M ), whose catalytic pocket has been unmasked by activating mutations, we successfully reconstituted in vitro polymerization of the cognate major pilin (SpaA). Mass spectrometry, electron microscopy, and biochemical experiments authenticated that SrtA 2M synthesizes pilus fibers with correct Lys-Thr isopeptide bonds linking individual pilins via a thioacyl intermediate. Structural modeling of the SpaA-SrtA-SpaA polymerization intermediate depicts SrtA 2M sandwiched between the N- and C-terminal domains of SpaA harboring the reactive pilin and LPXTG motifs, respectively. Remarkably, the model uncovered a conserved TP(Y/L)XIN(S/T)H signature sequence following the catalytic Cys, in which the alanine substitutions abrogated cross-linking activity but not cleavage of LPXTG. These insights and our evidence that SrtA 2M can terminate pilus polymerization by joining the terminal pilin SpaB to SpaA and catalyze ligation of isolated SpaA domains in vitro provide a facile and versatile platform for protein engineering and bio-conjugation that has major implications for biotechnology.
Department of Microbiology and Molecular Genetics, University of Texas Health Science Center, Houston, TX 77030; firstname.lastname@example.org email@example.com.