Title: In vitro reconstitution of sortase-catalyzed pilus polymerization reveals structural elements involved in pilin cross-linking

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 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). Further, 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 notmore » 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.« less

Authors:

Chang, Chungyu ^[1]; Amer, Brendan R. ^[2]; Osipiuk, Jerzy ^[3]; McConnell, Scott A. ^[2]; Huang, I-Hsiu ^[4]; Hsieh, Van ^[2]; Fu, Janine ^[2]; Nguyen, Hong H. ^[2]; Muroski, John ^[2]; Flores, Erika ^[1]; Ogorzalek Loo, Rachel R.  ^[2];

• Search DOE PAGES for author "Ogorzalek Loo, Rachel R."
• Search DOE PAGES for ORCID "0000-0002-0580-2833"

Loo, Joseph A. ^[2]; Putkey, John A. ^[1]; Joachimiak, Andrzej ^[3]; Das, Asis ^[5]; Clubb, Robert T. ^[2]; Ton-That, Hung  ^[1]

• Search DOE PAGES for author "Ton-That, Hung"
• Search DOE PAGES for ORCID "0000-0003-1611-0469"

---

+ Show Author Affiliations

1. Univ. of Texas Health Science Center, Houston, TX (United States)
2. Univ. of California, Los Angeles, CA (United States). Dept. of Chemistry and Biochemistry and UCLA-DOE Inst. for Genomics and Proteomics
3. Argonne National Lab. (ANL), Argonne, IL (United States); Univ. of Chicago, IL (United States)
4. National Cheng Kung Univ., Tainan (Taiwan)
5. Univ. of Connecticut Health Center, Farmington, CT (United States)

Publication Date:

Tue May 29 00:00:00 EDT 2018

Research Org.:

Argonne National Lab. (ANL), Argonne, IL (United States)

Sponsoring Org.:

USDHHS; National Institutes of Health (NIH); National Institute of Allergy and Infectious Diseases (NIAID); Center for Structural Genomics of Infectious Diseases (CSGID); National Institute of General Medical Sciences (NIGMS); National Institute of Dental and Craniofacial Research (NIDCR)

OSTI Identifier:

1464631

Grant/Contract Number:  

AC02-06CH11357; AI52217; HHSN272201200026C; HHSN272201700060C; GM103479; DE017382; DE025015

Resource Type:

Accepted Manuscript

Journal Name:

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

Additional Journal Information:

Journal Volume: 115; Journal Issue: 24; Journal ID: ISSN 0027-8424

Publisher:

National Academy of Sciences

Country of Publication:

United States

Language:

English

Subject:

59 BASIC BIOLOGICAL SCIENCES; Corynebacterium diphtheriae; pilus polymerization; protein ligation; sortase; transpeptidation