Andreas Holzenburg
Director, Microscopy and Imaging Center
Professor, Dept. of Biology
Professor, Dept. of Biochemistry and Biophysics

Focus: Microscopy and Imaging

Phone: 979-845 1164            
Fax:     979-847 8933
Office:  ILSB 1137

Curriculum Vitae
Personal Website

Best Known For:

Deciphering chloroplast division
FtsZ plays a pivotal role in the division of prokaryotic cells as well as plastids. One of the functional characteristics of FtsZ is its auto-assembly into a ring-like macromolecular complex called the Z-ring. During cell division, the Z-ring undergoes continuous and rapid remodeling via subunit exchange and constricts at the leading edge of the septum with the simultaneous loss of subunits. Consistent with the endosymbiotic origin of chloroplasts, plants possess nuclear-encoded, plastid-targeted homologues of bacterial FtsZ. However, whereas most prokaryotes, including the cyanobacterial relatives of chloroplasts, have a single form of FtsZ, two structurally and functionally distinct FtsZ protein families, FtsZ1 and FtsZ2, emerged in plants. Overall, the molecular mechanism of FtsZ filament assembly and its regulation, the structures of assembled protofilaments, and the structure of the in vivo FtsZ ring in chloroplasts remain poorly understood. Our overall goal is to expand the current model for FtsZ assembly and investigate and define the molecular structure and assembly dynamics of FtsZ rings in chloroplasts of Arabidopsis thaliana with the view to understand chloroplast size control. Modulation of the size of storage plastids (amyloplasts) and the starch granule size by changing the levels of FtsZ expression is of considerable interest to the chemical feedstock and food industry since increased starch granule size improves the wet-milling efficiency and thus the starch yield in staple crops.

Optimizing the quantum efficiency of photovoltaics using a biomimetic-computational approach
The most effective circumnavigation of the challenges arising from responding to the economics and politics of climate change is achieved by utilizing non-fossil sustained energy sources. Sunlight is a huge source of energy, amounting to 120,000 TW/year. Tapping into this energy resource means being able to effectively use it. Currently, the most advanced low-cost organic solar cells have a quantum efficiency of approximately 10%. This is in stark contrast to plant/ bacterial light-harvesting systems which offer a quantum efficiency of approx. 95%. To this end, the biomimetic project is concerned with how one could develop highly efficient photovoltaic devices from man-made materials. Of particular interest in this regard is the highly effective quantum coherence-enabled energy transfer. Noting that quantum coherence is promoted by charged residues and local dielectrics, classical atomistic simulations and time-dependent density functional theory (td DFT) are used to identify charge/dielectric patterns and electronic coupling at energy transfer interfaces. These interfaces have to be accurately defined both in terms of their chemistry and their locale. The latter is particularly critical as locations, distances, distances, orientations matter across the scales and vary in response to the environment. The calculations make use of structural information obtained on photosynthetic protein-pigment complexes while still in the native membrane as elucidated by electron crystallography. This way it may be possible to establish a link between supramolecular organization and quantum coherence in terms of what length scales enable fast energy transport and prevent quenching. Calculating energy transfer efficiencies between components based on different proximities will permit the search for patterns that enable defining material properties suitable for advanced photovoltaics. This project is in collaboration with Dr. Lisa Perez (Laboratory for Molecular Simulation, Dept. Chemistry).

Enabling phage-based therapies
Here the aim is to develop a thorough understanding of phage-induced bacterial lysis. When bacteria are attacked by bacteriophages, the biggest challenge for the phage is about egress in order to set its progeny free. So far, using microscopy in conjunction with biochemical and molecular biology approaches, it became clear that the inner membrane is lysed by holins, the peptidoglycan by endolysins, and the outer membrane likely by spanins. The latter step still remains to be further elucidated. Understanding the entire process at the molecular level will aid the development of new antibiotics in the age of ever-increasing resistances. This project is a long-term collaboration with Dr. Ryland Young (Dept. Biochemistry and Biophysics).

Cold microwave technology (CMT)
Last but not least in situ electron microscopy has, as a byproduct, enabled paving the way for CMT-enhanced diagnostics with the aim to further optimize antibody-antigen recognition and binding. This is particularly important with commercial ELISAs as these are very time consuming. Using CMT could revolutionize clinical routines in human and veterinary diagnostic laboratories and recent CMTe ELISA test results suggest that this may become a high impact technology for more readily sustained screening.

Last updated:  06 January 2013