Development of Chemical Strategies for Specifically Probing and Identifying Sulfur Carrier Proteins and Vitamin B6-Dependent Enzymes in Bacteria

Activity based protein profiling (ABPP) is a functional proteomic technology that uses chemical probes to detect mechanistically related classes of enzymes. Chemically probing a certain class of proteins helps to understand their biological function as a group, and discover new biosynthetic pathways for drug design. This research describes two activity based proteomic methods that have been developed to probe and identify sulfur carrier proteins and vitamin B6 dependent proteins, respectively. Sulfur carrier proteins are small proteins (<10 kDa) involved in pathways for efficient sulfur delivery. A chemical probe with sulfonyl-azide functional group was designed to label and identify the sulfur carrier proteins through a thioacid-azide reaction. This method identified a new sulfur carrier protein in Streptomyces coelicolor. Further study of its biological function led to the discovery and characterization of a new pathway of homocysteine formation, which is probably another direct sulfurylation of methionine biosynthesis. Vitamin B6 dependent proteins are a class of enzymes that cover a wide range of cellular functions such as transamination, racemization, and decarboxylation. Also, vitamin B6 dependent proteins have a critical role in human disease and the metabolic pathways of pathogens and plants. We used Escherichia coli as a model system to develop both radioactive and nonradioactive based methods to probe and identify vitamin B6 containing proteins in the bacterial proteome. This technique was then used to study how vitamin B6 proteins are regulated in response to cellular stress

Reduction of noise in medullary renograms from dynamic MR images

Dynamic magnetic resonance images of the kidney can be used to acquire separate renograms of the cortex and medulla, A high-quality cortical renogram can be determined directly from a region of interest (ROI) placed in the cortex. Due to partial volume effects, part of the signal from a ROI placed in the medulla is caused by cortical tissue, By subtracting a fraction of the cortical signal from the cortico-medullary signal, a purer medullary renogram can be obtained. A side effect of this subtraction is an increase in noise level. The noise level increases with larger partial volume fractions. Using a matched image filter, it is possible to exclude those areas from the ROI that have a high partial volume content, thus reducing the amount of cortical signal that has to be separated from the medullary signal, Noise reductions of up to 50% have been achieved in the medullary renogram, with an average reduction of 23%. (C) 2000 Wiley-Liss, Inc.</p

Reduction of noise in medullary renograms from dynamic MR images

Dynamic magnetic resonance images of the kidney can be used to acquire separate renograms of the cortex and medulla, A high-quality cortical renogram can be determined directly from a region of interest (ROI) placed in the cortex. Due to partial volume effects, part of the signal from a ROI placed in the medulla is caused by cortical tissue, By subtracting a fraction of the cortical signal from the cortico-medullary signal, a purer medullary renogram can be obtained. A side effect of this subtraction is an increase in noise level. The noise level increases with larger partial volume fractions. Using a matched image filter, it is possible to exclude those areas from the ROI that have a high partial volume content, thus reducing the amount of cortical signal that has to be separated from the medullary signal, Noise reductions of up to 50% have been achieved in the medullary renogram, with an average reduction of 23%. (C) 2000 Wiley-Liss, Inc