Robert C. Dunn

Dunn Research Group Poster

The recent emergence of single molecule detection and spectroscopy combined with the continued development in scanning probe techniques offers unique opportunities for probing complex biological systems at the single protein level.We are currently utilizing high resolution techniques such as confocal microscopy, atomic force microscopy (AFM), and near-field scanning optical microscopy (NSOM) to probe the structure and dynamics of membranes and membrane bound protein channels.In support of these projects is an ongoing effort in our group to develop new optical techniques and fiber optic sensors that provide expanded capabilities and tools with which to probe these important systems.For instance, we have recently developed a new form of microscopy based on energy transfer; we are currently fabricating nanometric light sources onto the end of AFM probes for high resolution optical measurements; and we are actively developing nanometer fiber optic chemical sensors for the detection of ions through single protein channels.The following provides brief examples of some of the research being conducted on model membranes and protein channels in our group.

Pulmonary Lung Surfactant

Respiratory distress syndrome (RDS) is the fourth leading cause of infant mortality in the United States and arises from an insufficiently developed lung surfactant.The lung surfactant is a complex mixture of lipids and proteins that coats the inner surface of the lungs.Healthy lung surfactant reduces the alveolar surface tension to near zero and therefore facilitates breathing by stabilizing the large surface area changes associated with respiration.In RDS, the absence of key proteins reduces the surfactant collapse pressure (i.e., compressibility) and the ability of the monolayer to respread during the breathing cycle, resulting in labored breathing, reduced oxygen transport, and often death in those afflicted.

Our laboratory is actively involved in using model membrane systems to understand the more complex natural biological membranes.For instance, we have recently found that the addition of surfactant protein B, one of the key proteins present in healthy surfactant, to model membranes of palmitic acid can induce critical behavior.This is interesting when one considers that large density fluctuations are associated with critical behavior which may provide clues into how healthy lung surfactant stabilizes the large volume changes associated with breathing.Projects with model membranes are ongoing to study the role of the surfactant proteins in membrane stability and to explore small molecule analogs that may be useful in the treatment of RDS.

Channel Dynamics

The nuclear pore complex (NPC) is a very large complex of proteins that forms the only known passageway across the nuclear membrane in cells.All material transported between the cytoplasm and nucleoplasm must pass through these channels which makes understanding the mechanisms involved in transport enormously important.

AFM image of a single nuclear pore channel

Currently, we are using the single molecule techniques in our laboratory to understand the origin of a large conformational change in the NPC that seems to be tied to the presence of calcium in the nuclear envelope.When the calcium stores in the nuclear envelope are depleted, AFM images of the cytoplasmic side of the NPC reveal the emergence of a “plug” in the center of the NPC.We are trying to use AFM in conjunction with the other high resolution techniques in our laboratory to understand both the identity of the plug and the biological significance of the conformational motion.We have recently developed a technique for imaging the NPCs with AFM under physiological conditions which opens the possibility of following the conformational motion in real time.We have also begun preliminary studies aimed at following the transport of DNA/lipid packages through a single NPC for applications in gene therapy.