Exploring Antibiotic Resistance in a Nanodisc

July 22, 2016

The increasing prevalence of antibiotic-resistant bacteria is a growing public health threat that must be addressed. One way that bacteria become resistant to antibiotics is through the use of multidrug transporters, membrane proteins that pump foreign molecules out of the cell. Thus, understanding how these proteins work could lead to the design of new drugs that can prevent this mechanism of antibiotic resistance. To this end, Basic Sciences investigator Hassane Mchaourab in collaboration with Cédric Govaerts (Université Libre de Bruxelles) has investigated the structural basis for the action of the Lactococcus lactis multidrug transporter LmrP, which exchanges a wide range of positively charged molecules in exchange for a proton. Their work builds on prior studies of the movement of LmrP upon substrate or proton binding. This work provided important insight into the function of the protein, but the investigators were concerned that their use of detergent to solubilize LmrP placed the protein in a nonphysiological environment. In their new work, the researchers studied the motions of LmrP in membrane nanodiscs to more closely mimic the protein’s natural state. Their results mostly agreed with the prior findings; however in the nanodisc, the protein’s motions occurred in a more physiological pH range and the key amino acids that coordinated the motions were more tightly coupled than in the detergent environment. This was likely due to a tight interaction between the protein and lipids in the membrane. The results provide key insights into the function of a prototypical multidrug transporter and demonstrate the importance of carrying out experiments such as these under conditions that resemble the natural environment as closely as possible. The work is published in the journal Nature Structural and Molecular Biology [C. Martens, et al. (2016), Nat. Struct. Mol. Biol., published online July 11, doi: 10.1038/nsmb.3262].

A Bridge to Better Motor Coordination

July 21, 2016

In the nervous system, signals are transmitted from cell to cell by the flow of chemical neurotransmitters across a specialized junction known as a synapse. In the vertebrate central nervous system, the major neurotransmitter at excitatory synapses is glutamate, which acts by binding to specific protein receptors expressed on the membrane of the post-synaptic neuron. Although the role of glutamate receptors in transmitting signals is well known, recent work shows that these proteins also contribute to the formation and structure of the synapse itself. In particular, GluD glutamate receptors bind to proteins called neurexins on the presynaptic neuron via a third protein, cerebellin-1. To better understand the importance of this inter-neuronal protein bridge, Basic Sciences investigator Terunaga Nakagawa and colleagues Michisuke Yuzaki (Keio University) and Radu Aricescu (University of Oxford) studied crystal structures of the complex-forming regions of GluD and cerebellin-1. Their results revealed key amino acids in the two proteins that are responsible for the binding interaction, allowing the investigators to test the importance of the interaction in vivo using mice genetically engineered to specifically prevent GluD-cerebellin-1 bridge formation. The results show that the GluD-cerebellin-1 interaction is critical to synapse development in the cerebellum and to the actual proper function of GluD during neurotransmission. This discovery provides important insight into the control of motor coordination in the cerebellum. The work is published in the journal Science [J. Elegheert, et al. (2016), Science, 353, 295].


Image attribution:
Figure reproduced from Wikimedia Commons (author BruceBlaus) under the Creative Commons Attribution-Share Alike 4.0 International license.


In Search of Cancer Drivers

July 21, 2016

Rapid advances in our ability to comprehensively examine cancer genomes have revealed that cancer results from an accumulation of genetic damage that is unique for each tumor. Consequently, new therapies that directly target abnormalities in cancer cells must be personalized to match the singular genetic composition of an individual patient’s cancer. To achieve this goal, new ways must be found to rapidly assess genomic damage in tumors and identify those that drive malignant behavior. To meet this challenge, Basic Sciences investigator Ian Macara and his laboratory have devised a new screen to rapidly assess clinically important genetic abnormalities in breast cancer. Their screen exploits the fact that mouse breast stem cells can grow and develop into complete mammary glands when transplanted into a mouse of the same genetic background. Using cells from mice genetically predisposed to breast cancer results in development of tumors in the transplanted glands after period of about 9 months. The Macara lab developed a way to rapidly screen up to 1000 genes normally involved in cell growth and signaling for their ability to make tumors appear in transplanted glands more rapidly. Their approach identified five genes that drive the more rapid growth of breast cancer in this model. More detailed examination of one of these genes (GTF2IRD1) revealed how it influences cell growth and confirmed that it is associated with aggressive breast, lung, and ovarian cancer in human patients. This new assay provides an important foundation from which to explore the full range of genes that drive breast cancer. The work is published in the journal Cell Reports [Y. Huo, et al. (2016), Cell Rep., 15, 2089].

Exploring the MiRNA-Cancer Connection

July 20, 2016

MicroRNA (miRNA) is a short strand of RNA that regulates the translation of messenger RNAs into proteins inside the cell. Recent evidence shows that miRNAs are also found outside of the cell, and that they likely play a role in cell-to-cell communications, including communications between cancer cells and the cells in their environment. To better understand the role that miRNA may play in cancer growth and metastasis requires knowledge of how it is exported out of the cell and how that export is regulated. Now, Basic Sciences investigator Alissa Weaver and her laboratory show that miRNA is exported in vesicles called exosomes in conjunction with the protein Argonaute 2 and that export is controlled by KRAS, a signaling protein that is known to be associated with many forms of cancer. This exciting discovery provides critical insight into the connection between miRNA, KRAS, and cancer and may ultimately point to new therapeutic targets for cancers in which miRNAs play an important role. The work is published in the journal Cell Reports [A. J. McKenzie, et al. (2016), Cell Rep., 15, 978].


Image attribution:
Figure reproduced under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International license from A. J. McKenzie, et al. (2016), Cell Rep., 15, 978.