Using PhADE in single molecule fluorescence imaging

Anna Loveland, a postdoc in the Grigorieff Lab, has a new paper, A general approach to break the concentration barrier in single-molecule imaging” that appeared today in Nature Methods online. The paper is based on her PhD work, which was done jointly in the labs of Antoine van Oijen and Johannes Walter at Harvard.

Single-molecule fluorescence imaging is often incompatible with physiological protein concentrations, as fluorescence background overwhelms an individual molecule’s signal. Loveland et al. employ a new imaging approach called PhADE (photoactivation, diffusion and excitation). A protein of interest is fused to a photoactivatable protein (mKikGR) and introduced to its surface-immobilized substrate. After photoactivation of mKikGR near the surface, rapid diffusion of the unbound mKikGR fusion out of the detection volume eliminates background fluorescence, whereupon the bound molecules are imaged. The authors labeled the eukaryotic DNA replication protein flap endonuclease 1 with mKikGR and added it to replication-competent Xenopus laevis egg extracts. PhADE imaging of high concentrations of the fusion construct revealed its dynamics and micrometer-scale movements on individual, replicating DNA molecules. Because PhADE imaging is in principle compatible with any photoactivatable fluorophore, it should have broad applicability in revealing single-molecule dynamics and stoichiometry of macromolecular protein complexes at previously inaccessible fluorophore concentrations.

Anna B Loveland, Satoshi Habuchi, Johannes C Walte & Antoine M van Oijen (2012) A general approach to break the concentration barrier in single-molecule imaging. Nature Methods

Riboswitches and fluoride

Ronald Breaker (Yale and HHMI) gave an inspiring talk today to kick off this year’s Biochemistry-Biophysics Friday Lunchtime Pizza Talks series, discussing his lab’s work on Riboswitches: Biology’s Ancient Regulators. If you missed the talk, here’s a review that might help you catch up.

Breaker ended the talk by discussing the fluoride-sensing riboswitch, and pointing to the new avenues for research to which this called attention. Coincidentally(?), a new paper in PNAS is out today from Chris Miller‘s lab here at Brandeis on exactly that — take a look at Stockbridge et al., Fluoride resistance and transport by riboswitch-controlled CLC antiporters.


Tenure track faculty position, Biochemistry

The Department of Biochemistry at Brandeis University invites applications for a tenure-track faculty position, to begin Fall, 2013. We are searching for a creative scientist who will establish an independent research program and who in addition will maintain a strong interest in teaching Biochemistry at the undergraduate and graduate levels. The research program should address fundamental questions of biological, biochemical, or biophysical mechanism.

Brandeis University offers the rare combination of a vigorous research institution in a liberal-arts college setting. The suburban campus is located 20 minutes from Boston and Cambridge and is part of the vibrant community of academic and biotechnology centers in the Boston area.

The application should include a cover letter, curriculum vitae, statement of research accomplishments and future plans, and three letters of reference. Applications will be accepted only through Additional inquiries may be directed to Chris Miller, Professor of Biochemistry (

First consideration will be given to applications received by December 1, 2012. Brandeis University is an Equal Opportunity Employer, committed to building a culturally diverse intellectual community. We particularly welcome applications from women and minority candidates.

What a failed drug does (and is there hope for latrepirdine?)

Latrepirdine (Dimebon) was initially used as an antihistamine drug in Russia. It was later found to be neuroprotective, and entered phase II clinical trials in the US for both Alzheimer’s disease and Huntington’s disease. However, Dimebon failed in a US-based phase II replication trial of a prior successful Russian phase II trial of mild-to-moderate AD. Given the initial promise of the drug and split results,  as well as the lack of treatments for neurodegenerative diseases, there in is significant interest in understanding the underlying molecular mechanism(s) for the drug’s effects.

In a paper appearing this week in Molecular Psychiatry, Brandeis researchers in the Petsko-Ringe lab, including postdoc Shulin Ju and undergraduate Jessica Liken ’11, used yeast models of neurodegenerative disease associated proteins to show that Dimebon specifically protects yeast from the cytotoxiciy of α-synuclein, a protein involved in Parkinson’s disease. They further showed that protection is mediated through its up-regulation of autophagy pathway. In collaboration with Sam Gandy‘s group at Mount Sinai School of Medicine, these findings were further confirmed and validated in neuronal cell and animal models.

Given these observations, disparities in the contribution of α-synuclein to the neuropathology between the Russian and US Dimebon studies might also explain, at least in part, the inconsistency of the cognitive benefit in the two trials. If this speculation is correct, then it may be interesting to test for benefits of Dimebon in treating synucleinopathies such as Parkinson’s disease, Lewy body dementia, REM sleep disorder and/or multiple system atrophy.

see also: press release from Mt. Sinai Alzheimer’s Diesease Research Center

Steele JW (*), Ju S(*), Lachenmayer ML(*), Liken J, Stock A, Kim SH, Delgado LM, Alfaro IE, Bernales S, Verdile G, Bharadwaj P, Gupta V, Barr R, Friss A, Dolios G, Wang R, Ringe D, Protter AA, Martins RN, Ehrlich ME, Yue Z, Petsko GA, Gandy S. Latrepirdine stimulates autophagy and reduces accumulation of alpha-synuclein in cells and in mouse brain. Molecular psychiatry. 2012.

Steele JW(*), Lachenmayer ML(*), Ju S, Stock A, Liken J, Kim SH, Delgado LM, Alfaro IE, Bernales S, Verdile G, Bharadwaj P, Gupta V, Barr R, Friss A, Dolios G, Wang R, Ringe D, Fraser P, Westaway D, St George-Hyslop PH, Szabo P, Relkin NR, Buxbaum JD, Glabe CG, Protter AA, Martins RN, Ehrlich ME, Petsko GA, Yue Z, Gandy S. Latrepirdine improves cognition and arrests progression of neuropathology in an Alzheimer’s mouse model. Molecular psychiatry. 2012.

Unraveling mutations in pediatric brain cancer

Medulloblastoma is the most common malignant brain tumor of childhood, with an overall mortality of 40 to 50 percent. Surviving children often have significant long-term cognitive and physical sequelae resulting from existing treatments. Therefore, identifying and understanding the genetic events that drive these tumors is critical for the development of more effective therapies.

In the 2 August issue of the journal Nature, Brandeis Biochemistry faculty member Daniel Pomeranz Krummel contributed his structural biological expertise in collaboration with colleagues at Children’s Hospital Boston, Dana-Farber Cancer Institute, Harvard University, the Broad Institute (MIT), Stanford and the Hospital for Sick Children in Toronto. The paper titled, “Medulloblastoma exome sequencing uncovers subtype-specific somatic mutations,” unravels a landscape of mutations that are peculiar to medulloblastomas. This paper represents a landmark study of medulloblastomas. More specifically, Pomeranz Krummel’s collaborators noticed that a protein called DDX3X had numerous mutations in medulloblastoma. Pomeranz Krummel was able to create a structural model of DDX3X that provided insight into the functional significance of the critical mutations in children with medulloblastoma (below, image).

DDX3X is an ATP-dependent RNA helicase. RNA helicases are fascinating proteins that function to drive the restructuring of RNA and/or RNA-protein assemblies, and have proven to be of great importance in cancer biology and HIV research. Pomeranz Krummel’s long-standing interest is in RNA-protein interactions and application of methods to visualize the enzymes critical to processing of RNA in the human cell. Thus, thinking about the structure-function relationship of this RNA helicase DDX3X was a problem of much interest to Pomeranz Krummel. This collaboration involved forging links between basic and translational scientists, thus giving rise to promising new horizons of treatment options for children with medulloblastoma.



Brandeis grad students guest edit The Biochemist

Brandeis graduate students Kene Piasta (Biochemistry, PhD ’11), Dharia McGrew (Mol. Cell. Biology, PhD ’11) and Lena Webb (Mol. Cell. Biology, MS ’11) were recently rewarded with the chance to be guest editors for The Biochemist, the bi-monthly magazine for members of the Biochemical Society. The issue they produced, with articles covering “The Science of Sensation“, is now available. The issue covers the biology of the five senses people have (and one that people don’t have but fish do). All three students have moved on from Brandeis: Lena now edits scripts for the Journal of Visualized Experiments, Kene is a postdoc in Joseph Falke’s lab at U. Colorado, Boulder, studying bacterial two-component chemoreceptors, and Dharia is a science and technology policy fellow with the state of California.

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