B12 METABOLISM IN HUMANS By NICOLE AURORA LEAL A ...

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24 diagnosed with the cblE disorder and 28 individuals with the cblG disorder (Fenton and Rosenberg 2000). Members of the cblE complementation group are deficient in methionine synthase activity due to a block in CH3Cbl formation. Fibroblast extracts from patients with this disorder had normal methionine synthase activity when high concentrations of reducing agent were added to the assay, but activity was reduced or absent when the reducing agent was used at lower concentrations (Watkins and Rosenblatt 1988). From these studies it was shown that the cblE group is defective in cobalamin reduction. The gene corresponding to this group was identified (MTRR) and localized to chromosome 5p15.2-p15.3 (Leclerc et al. 1998). The MTRR protein or MSR is required for the reductive activation of methionine synthase and was reviewed above (Wilson et al. 1999). The cblG complementation group is also deficient in methionine synthase activity but has normal levels of CH3Cbl. Fibroblast extracts from these patients were assayed and showed no MS activity under optimal conditions (Watkins and Rosenblatt 1989). This group is defined by defects in MS. Human MS is a modular enzyme with domains containing binding sites for homocysteine, CH3THF, SAM, and cob(II)alamin (Banerjee 1997). The cDNAs from cblG mutants have been analyzed and shown to contain missense and nonsense mutations (Leclerc et al. 1996). It appears that a majority of deficiencies in the cblG group are due to the lack of MS protein (caused by a premature stop codon due to nonsense mutations) and not in cobalamin binding. The clinical presentations of the cblE and cblG groups include homocystinuria without methylmalonic aciduria, developmental delay, megaloblastic anemia, and neurological disorders
(Watkins et al. 2002). Some patients respond to treatment with HOCbl (Watkins and Rosenblatt 2001). 25 Salmonella as a Model Organism for the Study of Cobalamin Metabolism Salmonella enterica is an important model organism for studies of <strong>B12</strong>-dependent processes (Schneider and Stroinski 1987, Roth et al. 1996). More is known about cobalamin metabolism and physiology in S. enterica than in any other single organism. Cobalamin transport, cobalamin biosynthesis, intramolecular rearrangements, and methyl transfer reactions have been investigated in S. enterica (Roth et al. 1996). In addition, S. enterica has a well-defined genetic system that includes methods for transformation, transduction, gene expression, directed, chemical, and transposon mutagenesis and a known genome sequence. One of the best-studied AdoCbl dependent enzymes in S. enterica is diol dehydratase. This enzyme is crucial for the metabolism of 1,2-propanediol. The genes required for growth of S. enterica on 1,2-propanediol are organized at the propanediol utilization (pdu) locus. Determination of the DNA sequence indicated that this locus has 23 genes (Bobik et al. 1997, Bobik et al. 1999): six pdu genes are thought to encode enzymes needed for the 1,2-propanediol degradative pathway (pduCDEPQW) (Bobik et al. 1997); two are involved in transport and regulation (pduF and pocR) (Bobik et al. 1992, Chen et al. 1994); two are probably involved in diol dehydratase reactivation (pduGH) (Bobik et al. 1999); one is needed for the conversion of cobalamin to AdoCbl (pduO) (Johnson et al. 2001); five are of unknown function (pduLMSVX); and seven share similarities to genes involved in the formation of carboxysomes (pduABJKNTU), polyhedral bodies found in certain cyanobacteria and chemoautotrophs (Shively and English 1991, Shively et al. 1998). The large number of genes required for the
Page 1 and 2: B12 METABOLISM IN HUMANS By NICOLE
Page 3 and 4: The work in this dissertation is de
Page 5 and 6: TABLE OF CONTENTS Page ACKNOWLEDGME
Page 7 and 8: General Molecular and Protein Metho
Page 9 and 10: LIST OF TABLES Table page 1-1. Aden
Page 11 and 12: 3-7. Stoichiometry of the MSR-ATR s
Page 13 and 14: DTT dithiothreitol E. coli Escheric
Page 15 and 16: Abstract of Dissertation Presented
Page 17 and 18: CHAPTER 1 INTRODUCTION History of C
Page 19 and 20: 3 (DMB). The DMB moiety is covalent
Page 21 and 22: 5 and deoxyadenosine. After hydroge
Page 23 and 24: 7 homocysteine recycling and methio
Page 25 and 26: methylmalonic acid. Methylmalonic a
Page 27 and 28: folate-dependent reactions includin
Page 29 and 30: tetanomorphum, P. shermanii, Euglen
Page 31 and 32: enzyme. This suggests that cob(II)a
Page 33 and 34: at the 5’-C of ATP by cob(I)alami
Page 35 and 36: iochemical studies and complementat
Page 37 and 38: 1997). Both cases of the cblD disor
Page 39: 23 The cblB complementation group i
Page 43 and 44: Chapter 2 of this dissertation repo
Page 45 and 46: Corrin Ring Dimethyl benzimidazole
Page 47 and 48: Classes Eliminases Dehydratases OH
Page 49 and 50: A) B) CH 3THF 33 MS-cob(I)alamin Me
Page 51 and 52: propanol dehydrogenase (PduQ) propa
Page 53 and 54: or from mutations that impair the a
Page 55 and 56: 1989). 5-bromo-4-chloro-3-indolyl-
Page 57 and 58: 41 5’-GCCGCCGGTACCGATGACGACGACAAG
Page 59 and 60: 43 Growth of Adenosyltransferase Ex
Page 61 and 62: anti-rabbit IgG (γ-chain specific)
Page 63 and 64: sequence similarity to a known ATR
Page 65 and 66: ATRs were produced as fusion protei
Page 67 and 68: 51 of the lacI repressor (not shown
Page 69 and 70: in which proteins bind B12, the "ba
Page 71 and 72: libraries may be particularly usefu
Page 73 and 74: 57 Figure 2-1. Multiple sequence al
Page 75 and 76: Table 2-2. Specific activities of b
Page 77 and 78: 61 1 2 3 4 5 25 kDa Figure 2-4. Wes
Page 79 and 80: 63 (cyanocobalamin, CNCbl) and hydr
Page 81 and 82: 65 5’- triphosphate (ATP), and di
Page 83 and 84: extracts of ATR 239K (160 mg protei
Page 85 and 86: Milford, MA). Samples (200 µl) wer
Page 87 and 88: Linearity of the ATR reaction 71 Th
Page 89 and 90: 73 reactions was characteristic of
Page 91 and 92:
75 MSR Produces little Cob(I)alamin
Page 93 and 94:
Johnson et al. 2001, Saridakis et a
Page 95 and 96:
AdoCbl by the MSR-ATR system. Exper
Page 97 and 98:
propionyl-CoA PCC (2S)-methylmalony
Page 99 and 100:
kDa 97 66 45 31 21 14 7 83 1 2 3 4
Page 101 and 102:
85 Table 3-3. The MSR-ATR system se
Page 103 and 104:
Absorbance 0.5 0.4 0.3 0.2 0.1 0.0
Page 105 and 106:
Wavelength, (525 nm) 0.24 0.23 0.22
Page 107 and 108:
Activity, (nmol min-1 Activity, (nm
Page 109 and 110:
al. 1988). The aldehyde is then dis
Page 111 and 112:
CoA-acylating propionaldehyde dehyd
Page 113 and 114:
97 previously published DNA sequenc
Page 115 and 116:
mM CHES (2-[N-cyclohexylamino]ethan
Page 117 and 118:
101 For the conjugation step, strai
Page 119 and 120:
103 from New England Biolabs (Bever
Page 121 and 122:
105 Propionaldehyde Dehydrogenase A
Page 123 and 124:
107 fraction. Following centrifugat
Page 125 and 126:
109 antiserum obtained was specific
Page 127 and 128:
111 biochemical evidence was presen
Page 129 and 130:
113 Table 4-1. Bacterial strains Sp
Page 131 and 132:
115 Table 4-3. Propionaldehyde dehy
Page 133 and 134:
kDa 209 80 49 35 29 117 1 2 3 4 Fig
Page 135 and 136:
CHAPTER 5 CONCLUSIONS In humans, co
Page 137 and 138:
121 substitutions that are common p
Page 139 and 140:
123 Studies also indicated that hum
Page 141 and 142:
LIST OF REFERENCES Aberg, A., S. Ha
Page 143 and 144:
127 Bradford, M. 1976. A rapid and
Page 145 and 146:
129 Fenton, W. A. and L. E. Rosenbe
Page 147 and 148:
131 Johnson, C. L. V. J., E. Pechon
Page 149 and 150:
133 Mellman, I., H. F. Willard and
Page 151 and 152:
135 Rossi, M., J. P. Glusker, L. Ra
Page 153 and 154:
137 Vlasie, M., S. Chowdhury and R.
Page 155 and 156:
BIOGRAPHICAL SKETCH Nicole Aurora L
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