Assist. Prof. Hasan DEMİRCİ
Koç University & Stanford Pulse Institute
TÜRKİYE
About Hasan: Dr. Hasan DeMirci is a member of the Biosciences Division at SLAC National Accelerator Laboratory and also affiliated with Non-Periodic Imaging group at Stanford PULSE Institute. He completed his B.S. at Bosphorus University in 2002 and later obtained a Ph.D. in Molecular Biology, Cell Biology and Biochemistry at Brown University in 2007.
Research: My research focuses on the structural biology of mutant prokaryotic ribosomes. I am interested in characterizing the function and dynamics of these mutants, with an eye toward answering questions in structure and dynamics of ribosomes which are resistant to some of today's commonly-used antibiotics. My current research efforts include methods development for ambient-temperature serial femtosecond X-ray crystallography (SFX) studies of ribosomes at next-generation lightsources like the Linac Coherent Light Source (LCLS) here at SLAC.
Recently, our latest work on a sample injector developed in-house by our group, the coMESH ("concentric microfluidic electric sample holder"), was published in Nature Methods. Using this method we were able to deliver microcrystals of 30S ribosomal subunits to the LCLS beam at ambient temperature, while kept in their native mother liquor. We solved the structure reported in the paper using several hundred (360) microliters of sample. In a previous preliminary paper (DeMirci et al., 2013), we used 10+ milliters of sample, and we had to choose between keeping my crystals in their unmodified mother liquor and using other sample delivery methods that had low flow rates. The emergence of coMESH meant we did not have to modify my crystals and we needed much less sample than before.
Based on our and others' additional experience using this sample injector, we are optimistic that we can use coMESH to deliver a wide variety of macromolecular crystals to an XFEL beam, meaning the features we benefited from can potentially place SFX within reach for many more biologists.
"Time-Resolved Serial Femtosecond X-ray Crystallographic Studies of Ribosome Complexes"
High-resolution ribosome structures determined by cryo X-ray crystallography have provided important insights into the mechanism of translation. Such studies have thus far relied on large ribosome crystals kept at cryogenic temperatures to reduce radiation damage. Here I will describe the application of serial femtosecond X-ray crystallography (SFX) using an X-ray free-electron laser (XFEL) to obtain diffraction data from ribosome microcrystals in liquid suspension at ambient temperature. 30S ribosomal subunit microcrystals programmed with decoding complexes and bound to either antibiotic compounds or their next-generation derivatives diffracted to beyond 3.4 Å resolution. Our results demonstrate the feasibility of using SFX to better understand the structural mechanisms underpinning the interactions between ribosomes and other substrates such as antibiotics and decoding complexes. We have also determined the structure of large (50S) ribosomal subunit in record-short time by using record-low amount of sample during and XFEL beamtime . This structure is the largest one solved to date by any FEL source to near-atomic resolution (3 MDa). We expect that these results will enable routine structural studies, at near-physiological temperatures, of the large ribosomal subunit bound to clinically-relevant classes of antibiotics targeting it, e.g. macrolides and ketolides, also with the goal of aiding development of the next generation of these classes of antibiotics. Overall, the ability to collect diffraction data at near-physiological temperatures promises to provide new fundamental insights into the structural dynamics of the ribosome and its functional complexes.
