R. Malcolm Brown, Jr.
| Title: | Professor, Johnson & Johnson Centennial Chair in Plant Cell Biology |  Video - PC Mac |
| Education: | Ph.D.: 1964, University of Texas | |
| Postdoc.: | The University of Texas at Austin | |
| Research: | Biosynthesis of cellulose; Golgi structure/function; high resolution light and electron microscopy | |
| Office: | PAI 2.34 | |
| Phone: | (512) 471-3364 Fax: (512) 471-3573 | |
| E-mail: | rmbrown@mail.utexas.edu | |
| Postal Address: | The University of Texas at Austin
Molecular Genetics & Microbiology
1 University Station A5000
Austin TX 78712-0162 |
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| Courses taught: | BIO 323L Laboratory Methods In Cell Biology | |
| Brown Laboratory home page: http://www.botany.utexas.edu/facstaff/facpages/mbrown/ | ||
I am interested in the mechanisms of biopolymer assembly, particularly the polymerization and crystallization reactions of cellulose. My current research in this area is to isolate and purify the enzymes responsible in cellulose biosynthesis from the cotton fiber, mung bean, Arabidopsis, selected algae, and Acetobacter. Once accomplished, these proteins will be sequenced (n-terminus or internal) and oligonucleotides prepared. Then we will identify, clone, and completely sequence the genes responsible for cellulose biosynthesis in these organisms as we have done for Acetobacter. We are concentrating especially on proteins that closely associate with cellulose synthases and modulate the assembly process. I am also interested in the molecular phylogeny of cellulose. A second project is the development of large scale industrial fermentation of microbial cellulose.
In addition to studying cellulose biosynthesis, I am using high resolution transmission electron microscopy (HRTEM) to provide novel images of molecules and macromolecular aggregates which include DNA, proteins, biopolymers, nanotubes, megatubes, and graphite.
2005 |
Cellulose biosynthesis: current views and evolving concepts.
Saxena IM, Brown RM Jr.
Ann Bot (Lond). 2005 Jul;96(1):9-21.
2004 |
Structural investigations of microbial cellulose produced in stationary and agitated culture.
Wojciech Czaja, Dwight Romanovicz and R. Malcolm Brown
Cellulose, 2004 Sept; 11(3,4):403-411.
The pivotal role of cyanobacteria in the evolution of cellulose synthases and cellulose synthase-like proteins
David R. Nobles and R. Malcolm Brown
Cellulose, 2004 Sept; 11(3,4):437 - 448
Formation of nematic ordered cellulose and chitin
Tetsuo Kondo, Wakako Kasai, R. Malcolm Brown
Cellulose, 2004 Sept; 11(3,4):463-474
Microfibrillar carbon from native cellulose
O. Ishida, D.-Y. Kim, S. Kuga, Y. Nishiyama and R. Malcolm Brown
Cellulose, 2004 Sept; 11(3,4):475-480
2003 |
Macromolecular structure of cellulose studied by second-harmonic generation imaging microscopy.
Brown RM Jr, Millard AC, Campagnola PJ.
Opt Lett. 2003 Nov 15;28(22):2207-9.
2002 |
2001 |
2000 |
Brown, Jr. R.M. and I.M. Saxena.
Plant Physiology and Biochemistry 38 (2000): 57-67.
ABSTRACT: This study provides an updated review of the current status on cellulose biosynthesis. The centerpiece of this work is the presentation of a new model of cellulose biogenesis. This model and its parts are presented for better understanding the mechanisms of polymerization and crystallization leading to biopolymer formation. The new information has been derived largely from sequence analysis, biochemistry, and ultrastructural data relating to cellulose, Nature's most abundant macromoleule.A Novel Cotton Ovule Culture: Induction, Growth, and Charcterization of Submerged Cotton Fibers (Gossypium hirsutum L.)
Rong Feng and R. Malcolm Brown, Jr.
In Vitro Cellular and Developmental Biology -- Plant 36 (2000): 293-299
ABSTRACT: The growth of submerged cotton (Gossypium hirsutum L.) fibers from cultured ovules has been investigated. The results indicate that exogenous plant hormone levels regulate the induction of submerged fiber growth. The age of ovules at induction is also important. Cell diameter, wall thickness, and cell length of submerged fibers were measured and compared with air-grown fibers and fibers grown in vivo (produced by cotton plants grown in the greenhouse). Various cell-wall thickening patterns were observed among submerged fibers, while only one predominant cell-wall deposition pattern was produced in air-grown fibers and in fibers produced in vivo. The diameter of submerged fibers was about the same as that of air-grown fibers but about 22% less than that of fibers grown in vivo. It appears that the secondary cell wall thickenings are initiated earlier in submerged fibers. The cell-wall thickness of submerged fibers, at 41 d post anthesis (DPA), was 51% greater than that of fibers grown in vivo, whereas the cell-wall thickness of air-grown fibers was 42% less than that of fibers produced in vivo. The cell length of submerged fibers was approximately half that of fibers grown in vivo, and the air-grown fiber length was about two-thirds of fibers grown in vivo. The age of ovules at induction affects the outcome of the air-grown fiber-cell length, but does not appear to affect the length of submerged fiber cells. To produce submerged fiber growth, we found that the optimal age of ovules at induction was 0 DPA, and the optimal medium (with a GA3 of 0.5 micromole and an IAA range of 5-20 micromole) depends on the time of ovule induction (-2 to + 2 DPA). We conclude that conditions leading to submerged cotton fiber growth have great potential for (a) direct monitoring of growth and making precise, detailed measurements during fiber growth and development; (b) producing cellulose and fibers in vitro more efficiently than earlier ovule-culture methods; and (c) using these unique cultures to obtain a better understanding of signal transduction and gene expression leading to growth, development, and programmed cell death in the life history of the cotton fiber.
1999 |
Kimura, S., Laosinchai, W., Itoh, T., Cui, X., Linder, R., and R. M. Brown, Jr.
The Plant Cell 11 (1999): 2075-2085.
ABSTRACT: The catalytic subunit of cellulose synthase is shown to be associated with the putative cellulose-synthesizing complex (rosette terminal complex [TC]) in vascular plants. The catalytic subunit domain of cotton cellulose synthase was cloned using a primer based on a rice expressed sequence tag (D41261) from which a specific primer was constructed to run a polymerase chain reaction that used a cDNA library from 24 days postanthesis cotton fibers as a template. The catalytic region of cotton cellulose synthase was expressed in Escherichia coli, and polyclonal antisera were produced. Colloidal gold coupled to goat anti-rabbit secondary antibodies provided a tag for visualization of the catalytic region of cellulose synthase during transmission electron microscopy. With a freeze-fracture replica labeling technique, the antibodies specifically localized to rosette TCs in the plasma membrane on the P-fracture face. Antibodies did not specifically label any structures on the E-fracture face. Significantly, a greater number of immune probes labeled the rosette TCs (i.e., gold particles were 20 nm or closer to the edge of the rosette TC) than did preimmune probes. These experiments confirm the long-held hypothesis that cellulose synthase is a component of the rosette TC in vascular plants, proving that the enzyme complex resides within the structure first described by freeze fracture in 1980. In addition, this study provides independent proof that the CelA gene is in fact one of the genes for cellulose synthase in vascular plants.Thermal stability of the cellulose synthase complex of Acetobacter xylinum.
Chen, H.P. and R. M. Brown, Jr.
Cellulose 6 (1999): 137-152.
ABSTRACT: The thermal stability of the cellulose synthase complex of A. xylinum has been analyzed in terms of enzyme activity loss as well as detection of its two major components (83kDa and 93 kDa polypeptides) in polyacrylamide gels under different electrophoretic sample treatment conditions. The cellulose synthase complex intrinsically is a thermally unstable enzyme and quickly loses its in vitro activity beyond 35 degrees C. The 83 kDa polypeptide has been found to be more labile than the 93 kDa polypeptide. When boiled in lithium dodecyl sulfate (LDS) buffer, the 83 kDa polypeptide is destroyed through peptide hydrolysis while the 93 kDa polypeptide remains uncleaved. The 83 kDa polypeptide is destroyed in LDS buffer at elevated temperatures beyond 55 degrees C. When boiled in the absence of LDS buffer, the 83 kDa polypeptide is completely aggregated while the 93 kDa polypeptide is only partially aggregated. In the absence of LDS buffer, the complete thermal aggregation of the 83 kDa polypeptide occurs at elevated temperatures beyond 85 degrees C. The aggregation process has been quantitatively analyzed by a newly-introduced quantitative index, Td (the temperature at which half the quantity of 83 kDa polypeptide disappears due to aggregation). The Td determined for the 83 kDa polypeptide in the product-entrapped fraction is 48 degrees C.
Are the reversibly glycosylated polypeptides implicated in plant cell wall biosynthesis non-processive beta-glycosyltransferases.
Saxena, I.M. and R. M. Brown, Jr.
Trends in Plant Science 4 (1999): 6-7.
Brown, Jr. R. M.
Pure and Applied Chemistry 71 (1999): 204-212.
Carbohydrate researchers may think it reasonable to believe that the synthesis and structure of a crystalline beta-1,4 glucan would be quite straightforward; however, this is not the case. The pitfalls and detours of research have been counterbalanced by exciting new discoveries in cellulose structure, biosynthesis, and molecular biology. Cellulose exists in crystalline and noncrystalline states, with the metastable cellulose I allomorph being the most abundant native crystalline form. Two stages of cellulose I crystallization will be described as well as a new form of ordered, noncrystalline cellulose known as quasi-tactic cellulose. The biosynthesis of cellulose is exceedingly complex, involving many genes and enzymes. Ordered membrane complexes (TCs) control the polymerization and crystallization to form cellulose microfibrils. Biochemical investigations have proven to be very difficult; however, recent breakthroughs on in vitro cellulose I assembly lend confidence that this part of cellulose research will soon yield great advances. The greatest success has come from molecular genetics research where the genes for cellulose biosynthesis from Acetobacter have been identified, cloned, mutated, and expressed in other systems. The multi-domain architecture of beta-glycosyl transferases has led to a better understanding of glucan chain polymerization leading to the twofold screw axis in cellulose as well as finding similar domains hypothesized to function in higher plant cellulose biosynthesis. The recent flurry of activity in this field promises to give even more clues to the developmental regulation of cellulose biosynthesis among plants, including the major textile and forest crops.GTPase activity and biochemical characterization of a recombinant cotton fiber annexin.
Shin, H. and R.M. Brown, Jr.
Plant Physiology 119 (1999): 925-934.
ABSTRACT: A cDNA encoding annexin was isolated from a cotton (Gossypium hirsutum) fiber cDNA library. The cDNA was expressed in Escherichia coli, and the resultant recombinant protein was purified. We then investigated some biochemical properties of the recombinant annexin based on the current understanding of plant annexins. An "add-back experiment" was performed to study the effect of the recombinant annexin on beta-glucan synthase activity, but no effect was found. However, it was found that the recombinant annexin could display ATPase/GTPase activities. The recombinant annexin showed much higher GTPase than ATPase activity. Mg2+ was essential for these activities, whereas a high concentration of Ca2+ was inhibitory. A photolabeling assay showed that this annexin could bind GTP more specifically than ATP. The GTP-binding site on the annexin was mapped into the carboxyl-terminal fourth repeat of annexin from the photolabeling experiment using domain-deletion mutants of this annexin. Northern-blot analysis showed that the annexin gene was highly expressed in the elongation stages of cotton fiber differentiation, suggesting a role of this annexin in cell elongation.
1998 |
He-Ping Chen and R.M. Brown, Jr.
Cellulose 5 (1998): 263-279.
Antibodies (anti-83 and anti-93) against the cellulose synthase complex from A. xylinum ATCC 53582 have been employed to study the evolutionary conservation of this enzyme complex among various A. xylinum strains, selected species of other cellulose-producing bacteria, algae, and vascular plants. Of the 18 A. xylinum strains examined, the 83 Kd polypeptide clearly is detected only in 4 strains while the 93 Kd polypeptide is observed in all 18 strains. Assuming that the revised acsAB gene (Saxena et al., 1994) encoding the 83 and 93 Kd polypeptides as a single polypeptide holds true for all A. xylinum strains, it is proposed that the cellulose synthase is conserved in A. xylinum but with varying degrees of homology. An unknown regulatory mechanism causing the degradation of the 83 Kd polypeptide in response to agitated culturing conditions has been suggested to explain the absence of the 83 Kd polypeptide in most of the Acetobacter strains examined. A. xylinum cellulose synthase appears to be conserved in phylogenetically related Rhizobium and Agrobacterium species, but not in algae and plants.
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