Harris Bernstein, Ph.D.


GBB
PROTEIN BIOGENESIS SECTION
NIDDK, National Institutes of Health
Building 5 , Room B120
5 Memorial Dr.
Bethesda, MD 20892
Tel: 301-402-4770
Fax: 301-496-9878
Email: harris_bernstein@nih.gov

Education / Previous Training and Experience:
B.A., Harvard University, 1980
Ph.D., Massachusetts Institute of Technology, 1987


Research Statement:
My laboratory has a long-standing interest in understanding how proteins are transported across the cell membranes of both pathogenic and non-pathogenic bacteria. In one project we are investigating the mechanism by which pathogenic Gram-negative bacteria secrete proteins via the “autotransporter” or “type V” pathway. Autotransporters are proteins that contain two domains, a large N-terminal extracellular domain ("passenger domain”) and a C-terminal β barrel domain (“β domain”) that is embedded in the outer membrane. The passenger domains of different members of the autotransporter superfamily play a variety of roles in pathogenesis; in some cases they function as adhesins, but in other cases they are cleaved from the cell surface and function as soluble virulence factors. After autotransporters are translocated across the cytoplasmic membrane by the Sec machinery, the passenger domain is transported across the outer membrane by an unknown mechanism. It was originally proposed that the passenger domain is secreted through a channel formed by the β domain to which it is covalently linked (whence the name “autotransporter”). Our recent results are inconsistent with this proposal, however, and suggest that the Bam complex, a heterooligomer that promotes the integration of β barrel proteins into the outer membrane, plays a key role in passenger domain secretion.

In a second project we are studying the regulation of expression of secA, a gene that encodes a major component of the bacterial Sec machinery. Expression of this gene is regulated at the level of translation by “ribosome stalling” or “translation arrest”. SecA is in an operon with secM, a gene that encodes a small secreted protein. When the secretion burden of the cell rises, the synthesis of the SecM protein stalls shortly before ribosomes reach the termination codon. Ribosome stalling alters the secondary structure of the secM-secA mRNA and leads to a concomitant increase in SecA synthesis. Our results indicate that the recognition of a SecM sequence motif inside the ribosome tunnel causes ribosome stalling. We are currently trying to understand how RNA and protein components of the ribosome tunnel recognize this motif and how detection of the motif generates a signal that alters ribosome function. We believe that elucidation of the mechanism of SecM stalling will yield insights into other ribosome stalling phenomena that have been observed in bacteria, fungi and higher eukaryotic cells.



Selected Publications:
1. Ieva R, Tian P, Peterson JH, Bernstein HD Sequential and spatially restricted interactions of assembly factors with an autotransporter β domain. Proc Natl Acad Sci U S A(108): E383-E391, 2011. [Full Text/Abstract]

2. Peterson JH, Tian P, Ieva R, Dautin N, Bernstein HD Secretion of a bacterial virulence factor is driven by the folding of a C-terminal segment. Proc Natl Acad Sci U S A(107): 17739-17744, 2010. [Full Text/Abstract]

3. Peterson JH, Woolhead CA, Bernstein HD The conformation of a nascent polypeptide inside the ribosome tunnel affects protein targeting and protein folding. Mol Microbiol(78): 203-217, 2010. [Full Text/Abstract]

4. Ieva R, Bernstein HD Interaction of an autotransporter passenger domain with BamA during its translocation across the bacterial outer membrane. Proc Natl Acad Sci U S A(106): 19120-19125, 2009. [Full Text/Abstract]

5. Yap MN, Bernstein HD The plasticity of a translation arrest motif yields insights into nascent polypeptide recognition inside the ribosome tunnel. Mol Cell(34): 201-211, 2009. [Full Text/Abstract]

6. Ieva R, Skillman KM, Bernstein HD Incorporation of a polypeptide segment into the beta-domain pore during the assembly of a bacterial autotransporter. Mol Microbiol(67): 188-201, 2008. [Full Text/Abstract]

7. Barnard TJ, Dautin N, Lukacik P, Bernstein HD, Buchanan SK Autotransporter structure reveals intra-barrel cleavage followed by conformational changes. Nat Struct Mol Biol(14): 1214-20, 2007. [Full Text/Abstract]

8. Dautin N, Barnard TJ, Anderson DE, Bernstein HD Cleavage of a bacterial autotransporter by an evolutionarily convergent autocatalytic mechanism. EMBO J(26): 1942-52, 2007. [Full Text/Abstract]

9. Dautin N, Bernstein HD Protein secretion in gram-negative bacteria via the autotransporter pathway. Annu Rev Microbiol(61): 89-112, 2007. [Full Text/Abstract]

10. Hegde RS, Bernstein HD The surprising complexity of signal sequences. Trends Biochem Sci(31): 563-71, 2006. [Full Text/Abstract]

11. Woolhead CA, Johnson AE, Bernstein HD Translation arrest requires two-way communication between a nascent polypeptide and the ribosome. Mol Cell(22): 587-98, 2006. [Full Text/Abstract]

12. Szabady RL, Peterson JH, Skillman KM, Bernstein HD An unusual signal peptide facilitates late steps in the biogenesis of a bacterial autotransporter. Proc Natl Acad Sci U S A (102): 221-6, 2005. [Full Text/Abstract]

13. Skillman KM, Barnard TJ, Peterson JH, Ghirlando R, Bernstein HD Efficient secretion of a folded protein domain by a monomeric bacterial autotransporter. Mol Microbiol(58): 945-58, 2005. [Full Text/Abstract]



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Page last updated: June 09, 2011

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