Research Projects
Identifying novel genes involved in anchoring neurons
SWTY is a novel peptide motif that directs cell surface expression
SWTY is a novel peptide motif that directs cell surface expression
Columbia University (Marty Chalfie Lab)
Image: A touch receptor neuron expressing green fluorescent protein (GFP).
Brian's postdoctoral research was on the sense of touch in the microscopic worm, C. elegans. Touch sensation involves translating mechanical forces into electrical signals in neurons. Other senses also based on mechanical forces include hearing, balance, and proprioception. Unlike sight, smell, and taste, the molecular building blocks for mechanical senses in humans have not been clearly identified. Brian's advisor, Martin Chalfie, identified many genes necessary for touch sensation in C. elegans by mutating the worms and selecting animals that could not sense touch. In the years since, many experiments have been performed to learn how these genes function.
The C. elegans nematode has six neurons responsible for sensing gentle touch. These touch receptor neurons (TRNs) have long axons that run along the body in an anterior/posterior fashion. Along the TRN axons, attachments anchor the cell to the hypodermis. Extracellular matrix proteins necessary for hypodermal attachment include MEC-1, MEC-5, and HIM-4. To better elucidate the structures responsible for TRN hypodermal attachment, Brian conducted a mutagenesis screen to identify more attachment genes. In addition, he demonstrated that MEC-5 is expressed in muscle cells, and that muscle cell expression is sufficient for touch sensitivity. MEC-5 is unique as a protein critical for touch sensation that is not expressed in TRNs themselves.
SWTY is a novel peptide motif that directs cell surface expression
SWTY is a novel peptide motif that directs cell surface expression
SWTY is a novel peptide motif that directs cell surface expression
Johns Hopkins University School of Medicine (Min Li Lab)
Image: Surface expression with SWTY-like motif (left) or absent with mutated SWTY-like motif (right).
Tight regulation of proteins expressed on the cell surface enables control of quantity and quality. Quantity regulation is important, because some proteins like ion channels can have large effects in small quantities. Quality control is critical, because many surface proteins function as multimeric complexes that must be assembled properly to function. Many cell surface proteins contain small signals in their amino acid sequence that enable regulation of their localization. These signals can be reverse (away from surface) like RXR, or forward (toward surface) like DXE.
In the Li Lab, Sojin Shikano identified a new synthetic C-terminal motif RGRSWTY-COOH (SWTY for short) that can override the RXR reverse signal. SWTY acts via binding to a protein called 14-3-3. While SWTY clearly was effective when added to proteins tested in cell cultures, we wanted to know whether similar motifs were found in nature. Brian used bioinformatics to identify candidate SWTY-like motifs in proteomes of a range of animals. He then tested the candidate motifs for forward transport function in cell cultures. Brian identified a functional SWTY-like motif in human GPR15, a G-protein coupled receptor. In additional work, he examined the relationship of the SWTY sequence with 14-3-3 binding. In the process, he collaborated with Meng Wu in developing a new fluorescence-based assay to detect 14-3-3 binding.