Neuroscience
Blocking Protein Might Reverse Hearing Loss
Cell Biology
Functional Protein Changes Caught and Quantified
Genomics
Gain and Loss of Amino Acids Detected Across All of Life
Ambulatory Care
A Third of Older People May Take
Potentially Inappropriate Medicines
Social Medicine
Past Research Enables Mental Health Services to Fill Gap for Tsunami Survivors
New Books
The Winter Bookshelf
Bacteria Exhibit Novel Method for Sensing Environment
Enzymes Used to Generate Diversity in Antibiotics
Thalamus Calcium Channel Supports a Sound Sleep
New Appointments to Full Professorships
Ten Students Named Schweitzer Fellows
Red Book Grants List to Be Posted Next Week
Congratulations to Training Institute Grads
Honors and Advances
Failing Elders Weigh Heavily on Reservation Families
Some Wrinkles of Delayed Residency
Bacteria Exhibit Novel Method for Sensing Environment
Michael Gilmore and his colleagues have discovered a new way for bacteria to sense and respond to their environment—from the human gut to the bloodstream, the eye, or a wound. Currently the acting CEO of Schepens Eye Research Institute and the Charles L. Schepens professor of ophthalmology at HMS, Gilmore reports the findings on the bacterium Enterococcus faecalis in the Dec. 24 Science.
The cytolysin produced by E. faecalis remotely senses target cells and increases toxin production. The two subunits of the bacterium’s cytolytic toxin, LL and LS, bind to one another and form an inactive complex if there are no target cells nearby (left). If target cells are present (right), LL binds more tightly to them than does LS. This leaves LS subunits unbound, and in this form, they can return to the bacterial membrane, signaling the presence of target cells. The cytolysin operon is thereby upregulated. (Illustration adapted by Rachel Meyer)
This particular enterococcus is a serious hospital-acquired infection that frequently sports resistance to multiple antibiotics. The organism sometimes produces a toxin that explodes erythrocytes and other human cells as well as gram-positive bacteria. The toxin kills these targets by punching holes through their membranes. In his research, Gilmore is seeking treatment options beyond antibiotics. “We look at infection as a process. Once we understand the critical points, we can try to intervene,” he said.
Like a suspicious homeowner laying traps for mice, E. faecalis continuously produces a small amount of its cytolytic toxin. Previous work by Gilmore and his colleagues showed that if there are no target cells around to trigger the traps, the bacteria frugally keep toxin production at low levels. They crank up output of the toxin if they detect their target cells or bacteria. But how do they know whether there are targets nearby?
Gilmore’s team investigated the genetics of E. faecalis and found that the toxin had two short proteins, regulated in concert with six other genes required to produce and secrete the active cell-exploding cytolysin. Team members found that mutating the gene for the larger toxin protein, LL, or dousing bacterial colonies with the smaller toxin component, LS, triggered increased toxin production. Gilmore therefore suspected that both subunits were involved in regulation of the cytolysin operon.
Experiments in solution showed that the subunits had an affinity for each other. Without target cells, they formed large, inactive complexes. In experiments in which the subunits attached to membranelike vesicles, the researchers found that while both subunits could bind to the target vesicles, LL bound more than six times as firmly as the smaller LS.
Gilmore concluded that if there are target cells in the environment, LL will bind to them, leaving LS free to loop back to a receptor, sending a signal to upregulate the operon (see diagram). Then toxin concentration rises and target cell membranes are lysed by both subunits working together. Gilmore sees applications in reducing the severity of antibiotic-resistant E. faecalis infections by interfering with its sensory system. He imagines the future possibility of engineering the operon to detect other targets. If the LL subunit could be modified to stick to minerals or to other bacteria, for example, the bacterial remote sensing system might serve in fields as diverse as mining and medicine.
—Tai Viinikka
Enzymes Used to Generate Diversity in Antibiotics
Antibiotic development is a race between human intelligence and bacterial evolution, and recently humans have been losing. Christopher T. Walsh would like to change that. Research by Walsh, first author Ryan Kruger, and colleagues, which appears in the January Chemistry & Biology, extends the lab’s “mix and match” approach to antibiotic development. The team’s strategy is to build new chemical “decorations” on known molecular backbones to yield drugs that are more effective against evolving bacteria.
Walsh, the Hamilton Kuhn professor of biological chemistry and molecular pharmacology, asked postdoctoral fellow Kruger to explore why the antibiotic teicoplanin kills some bacteria that are resistant to a very similar drug, vancomycin. Vancomycin has been used since the 1960s, and resistance to it is increasing. Teicoplanin, on the other hand, has only limited FDA approval. The two drugs are thought to confound the same cell wall–building process, raising the question of why one works when the other fails.
As glycopeptide antibiotics, vancomycin, teicoplanin, and a candidate drug called A-40,926 all share a similar backbone of amino acids, differing in chemical groups such as sugars and acyl chains that hang off the frame. Kruger used acid hydrolysis chemistry to cut the antibiotics down to their skeletons and then attached new chemical groups. He cloned enzymes from the bacteria that produce teicoplanin and A-40,926 and found that the enzymes could add a fatty tail (the acyl chain) to the vancomycin backbone. The team also varied the pH of the reaction and found that the enzyme would add an acyl chain in other, nearby positions on the molecule, producing novel products that may be particularly potent against certain bacteria.
Walsh’s combinatorial approach to chemoenzymatics could yield promising candidate antibiotics that may not occur in nature. It is also far cheaper and less difficult than trying to piece together complicated molecules from scratch—Kruger can buy most of the sugar and acyl-chain components off the shelf and relies on Harvard professor Daniel Kahne of the Department of Chemistry and Chemical Biology to build a few unusual add-ons. “Part of the goal here is to see what can be accomplished quickly and easily with enzymology, and what is best left for synthetic chemists,” Kruger said.
The question of why bacteria might succumb to teicoplanin but not vancomycin remains unanswered, but Kruger thinks that if a variety of molecules can be built to probe the system, the important details of their antibiotic action may become clear.
Thalamus Calcium Channel Supports A Sound Sleep
A Boston-centered research team has identified a molecular mechanism in the brain that may permit people to sleep through things that go bump in the night. Matthew Anderson, an HMS instructor in neurology at Beth Israel Deaconess Medical Center, is first author of the study, published in the Feb. 1 Proceedings of the National Academy of Sciences.
When people sleep, the brain mostly ignores the senses. This sensory gating has been attributed to the thalamus, because sensory inputs must travel through the thalamus before reaching the cortex. But hard evidence has been scarce. Previous work implicated a subset of calcium channels, dubbed CaV3.1. Anderson, working with Susumu Tonegawa’s lab at MIT, set out to investigate these unusual proteins.
The team created three mutant strains of mice. A global knockout lacked the CaV3.1 T-type channel entirely, and the team used Cre/loxP recombinase to create strains lacking the channel either in the cortex or the thalamus.
Observations found that thalamic knockouts and global knockouts suffered fragmented sleep, waking more often and experiencing shorter bouts of non-REM sleep than cortex knockouts or the wild type. Anderson then probed thalamic neurons in a thin slice of brain. “What we discovered is that the calcium channel can shut down a neuron for many seconds,” he said. In sleeping-state neurons, sensory signals triggered the calcium channels to open, and by an unknown mechanism, the calcium burst inhibited neuronal firing.
In Anderson’s lab at BID, figuring out how calcium from the channel shuts off neuronal firing is a priority. He also hopes to explore the role of this thalamic sensory gating mechanism in the control of pain and some forms of epilepsy.