Harvard University - Department of Molecular & Cellular Biology

ANDRES LESCHZINER

Leschziner
Associate Professor of Molecular and Cellular Biology

Email: aleschziner@mcb.harvard.edu
Phone: 617-496-2717

Mail: NW 311.15
Northwest Building
52 Oxford St
Cambridge, MA  02138

Leschziner Lab Homepage
Members of the Leschziner Lab
List of Publications from PubMed

Courses

MCB 56. Physical Biochemistry: Understanding Macromolecular Machines
Catalog Number: 5424  View Course Website
Term: Spring Term 2013-2014.   Credit: Half course.
Instructors: Rachelle Gaudet, Andres Leschziner
Course Level: Primarily for Undergraduates
Description: The course aims to develop fundamental concepts of biochemistry as they apply to macromolecules, including protein and nucleic acid structure, thermodynamics and kinetics, ligand interactions and chemical equilibria. The course will also emphasize how these concepts are used in studies of the structure and function of biological molecules, including examples from metabolism. In the weekly section, students will undertake a discovery-based laboratory research project in which they will apply these concepts toward understanding the structure and function of the ATPase domain from the ABC transporter associated with antigen processing (TAP).
Prerequisite(s): LPSA or LS1a, Chemistry 20/30 or Chemistry 17/27 (Chemistry 27 may be concurrent), Math 1b. A solid foundation in molecular and cellular biology (which could be provided by MCB 52 or MCB 54, for example) and/or physics (e.g. PS2) is recommended.
Meetings: M., W., F., at 10, and a weekly laboratory/discussion section.
MCB 293. Biochemistry, Chemical and Structural Biology
Catalog Number: 2706  View Course Website
Term: Fall Term 2013-2014.   Credit: Half course.
Instructors: Rachelle Gaudet, Andres Leschziner
Course Level: Primarily for Graduates
Description: This course will introduce basic principles in general, organic and physical chemistry, including kinetics and thermodynamics, as well as macromolecular structure. Concepts will be illustrated with examples taken from the visual system.
Note: Required for first year graduate students in the Molecules, Cells and Organisms (MCO) Training Program.
Meetings: M., W., 2-4
MCB 329. Structural Biology of ATP-Dependent Chromatin Remodeling
Catalog Number: 6060  View Course Website
Term: Fall Term; Repeated Spring Term 2013-2014.   Credit: Half course.
Instructor: Andres Leschziner
Course Level: Graduate Course
BIOPHYS 316. Structural Biology of ATP-Dependent Chromatin Remodeling
Catalog Number: 4680  View Course Website
Term: Fall Term; Repeated Spring Term 2013-2014.   Credit: Half course.
Instructor: Andres Leschziner
Course Level: Graduate Course
(View all MCB Courses)

Research

Structural Studies of Macromolecular Machines

We are interested in exploring the role played by conformational flexibility in the biological activity of macromolecular complexes. We approach this question with a combination of biochemical and structural approaches but focus, in particular, on cryo-electron microscopy (cryo-EM).

As part of our interest in conformational dynamics, my group is also involved in developing methodologies for electron microscopy, in particular as they relate to the generation of initial reconstructions from novel samples.

Cytoplasmic Dynein

Cytoplasmic dynein is the largest and most complex of the three cytoskeletal motors—dyneins, kinesins and myosins—with a basic motor unit consisting of a dimer of two identical 500kDa chains. We are interested in understanding how dynein moves processively along microtubules, specifically how it coordinates its multiple moving parts. We have recently focused on how the cycles of force-generating ATP hydrolysis, occurring in the ring-shaped AAA+ motor domain, are coupled to the cycles of microtubule binding and release, which occur at the microtubule binding domain, located at the end of dynein’s long “leg” (an antiparallel coiled-coil). These two cycles occur 25 nm away from each other, yet processivity depends critically on their coordination.

Dynein carries out an array of biological activities, transporting most cellular cargo from the periphery towards the cell interior and participating in aspects of chromosome segregation during cell division. Intriguingly, a single cytoplasmic dynein gene is responsible for all these activities, in contrast to the dozens of specialized kinesin and myosin genes that have evolved to fulfill their own functional diversity. It seems likely that dynein accomplishes this functional diversity through regulation. Our work is aimed at understanding the mechanistic basis of this regulation. We are currently focusing on Lis1, a ubiquitous dynein co-factor, which acts as a “clutch” to uncouple dynein’s cycles of ATP hydrolysis and microtubule binding and release. We are using structural approaches to understand how Lis1 does this.

[In collaboration with the Reck-Peterson lab, Dept. of Cell Biology, Harvard Medical School]

ATP-Dependent Chromatin Remodeling

The extreme degree of compaction of DNA into chromatin would seem to create an insurmountable barrier to all DNA transactions. However, a variety of mechanisms have evolved that allow cells to turn this apparent impediment into a highly dynamic and finely tuned regulatory device that controls the accessibility of specific DNA sequences. Many players are involved in achieving this regulation. A number of protein factors are involved in covalently modifying chromatin—either DNA itself or the histone octamer around which DNA is wrapped. Another group, the ATP-dependent chromatin remodeling complexes, utilizes the energy from ATP hydrolysis to non-covalently modify nucleosomes. These remodelers are large (often above 1 MDa) multi-subunit complexes (some with up to 15 different proteins) that are conserved from yeast to humans. Their activity leads to a number of different fates for the remodeled nucleosomes: sliding along DNA, transfer to a different DNA segment, formation of a “loose” nucleosome structure and exchange of histone components.

As it is the case for dynein, these large complexes have to coordinate conformational changes within their large structures in order to carry out their intricate reactions. Our goal is to understand, mechanistically, how these complexes interact with nucleosomes and orchestrate the motions required to remodel them. We have been using RSC, an essential remodeling complex from the yeast S.cerevisiae, as our model system.

[In collaboration with the Cairns lab, HHMI / University of Utah]

Electron Microscopy Reconstruction Methods

Our group is also interested in what remains a major challenge in Three Dimensional Electron Microscopy (3D EM)—obtaining initial models of novel samples. We developed a new reconstruction method (Orthogonal Tilt Reconstruction) that addresses some of the problems and limitations of existing approaches. We are interested in further developing this method to make the generation of initial models a robust and routine aspect of 3D EM.

Publications

Redwine WB, Hernandez-Lopez R, Zou S, Huang J, Reck-Peterson SL and Leschziner AE (2012). Structural basis for microtubule binding and release by dynein. Science 337(6101):1532-6

Huang J, Roberts AJ, Leschziner AE and Reck-Peterson SL (2012). Lis1 acts as a “clutch” between the ATPase and microtubule-binding domains of the dynein motor. Cell 150: 975-86

Leschziner AE (2011). Electron microscopy studies of nucleosome remodelers. Curr Opin Struct Biol 21(6): 709-18

Chandramouli P, Hernandez-Lopez R, Wang, HW and Leschziner AE (2011). Validation of the orthogonal tilt reconstruction method with a biological test sample. J Struct Biol 175: 85-96.

Leschziner A (2010). The orthogonal tilt reconstruction method. Methods Enzymol 482:237-62.

Leschziner AE, Saha A, Wittmeyer J, Zhang Y, Bustamante C, Cairns BR and Nogales E (2007). Conformational flexibility in the chromatin remodeler RSC observed by electron microscopy and the orthogonal tilt reconstruction method. Proc. Natl. Acad. Sci. USA 104(12): 4913-8.

Leschziner AE and Nogales E (2007). Visualizing flexibility at molecular resolution: Analysis of heterogeneity in single-particle electron microscopy reconstructions. Annu. Rev. Biophys. Biomol. Struct. Vol.36: 43-62.

Leschziner AE and Nogales E (2006). The Orthogonal Tilt Reconstruction method: an approach to generating single-class volumes with no missing cone for ab initio reconstruction of asymmetric particles. J Struct Biol. 153(3):284-99.

Leschziner AE, Lemon B, Tjian R and Nogales E (2005). Structural studies of the human PBAF chromatin-remodeling complex. Structure (Camb) 13(2): 267-75.

updated: 04/15/2014