The long range goal of this research is to gain insight into the selective transport of proteins from the cytoplasm into organelles with specialized metabolic functions. This work will focus on the import of proteins into the chloroplast. The chloroplast is one of the two energy producing organelles in eucaryotes. Like the mitochondrion, most of its proteins are encoded by the nuclear genome, synthesized as polypeptide precursors, transported across a membrane barrier, and proteolytically processed. These studies will lead to an understanding of the general principles used to correctly route proteins in the cell. The import pathway of the light-harvesting chlorophyll a/b binding protein (LHCP) will be investigated. The LHCP gene has been inserted into a transcription vector to generate RNA and subsequently, labeled LHCP precursor (pLHCP) in vitro. Modifications in the pLHCP gene will be made using recombinant DNA methods to generate corresponding changes in the primary structure of the precursor. This approach provides a means of obtaining mutants in chloroplast assembly not yet achieved by conventional genetics. In a cell-free system, restructured proteins will be synthesized and incubated with isolated chloroplasts to determine how these changes affect binding to the organelle's envelope, transport across the membrane, intraorganelle routing and, of particular interest, precursor processing. A soluble processing enzyme that cleaves pLHCP has been identified and partially purified. The processing reaction will be optimized, and the determinants for pLHCP cleavage will be determined. The enzyme will be purified to homogeneity by column chromatographic methods, which have already been started, to establish its molecular composition and specificity. A gene coding for the enzyme will be isolated from a complementary DNA library and sequenced to study the structure of the polypeptide and its biosynthetic pathway. Processing enzymes play an essential role in organelle biogenesis; they are responsible for releasing the mature, functional proteins within the organelle. This research will have relevance to correcting metabolic disorders.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM036419-08
Application #
2178351
Study Section
Cellular Biology and Physiology Subcommittee 1 (CBY)
Project Start
1986-04-01
Project End
1995-03-31
Budget Start
1993-04-01
Budget End
1995-03-31
Support Year
8
Fiscal Year
1993
Total Cost
Indirect Cost
Name
University of Chicago
Department
Genetics
Type
Schools of Medicine
DUNS #
225410919
City
Chicago
State
IL
Country
United States
Zip Code
60637
VanderVere, P S; Bennett, T M; Oblong, J E et al. (1995) A chloroplast processing enzyme involved in precursor maturation shares a zinc-binding motif with a recently recognized family of metalloendopeptidases. Proc Natl Acad Sci U S A 92:7177-81
Oblong, J E; Lamppa, G K (1992) Identification of two structurally related proteins involved in proteolytic processing of precursors targeted to the chloroplast. EMBO J 11:4401-9
Oblong, J E; Lamppa, G K (1992) Precursor for the light-harvesting chlorophyll a/b-binding protein synthesized in Escherichia coli blocks import of the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase. J Biol Chem 267:14328-34
Clark, S E; Lamppa, G K (1991) Determinants for cleavage of the chlorophyll a/b binding protein precursor: a requirement for a basic residue that is not universal for chloroplast imported proteins. J Cell Biol 114:681-8
Clark, S E; Oblong, J E; Lamppa, G K (1990) Loss of efficient import and thylakoid insertion due to N- and C-terminal deletions in the light-harvesting chlorophyll a/b binding protein. Plant Cell 2:173-84
Clark, S E; Abad, M S; Lamppa, G K (1989) Mutations at the transit peptide-mature protein junction separate two cleavage events during chloroplast import of the chlorophyll a/b-binding protein. J Biol Chem 264:17544-50
Lamppa, G K (1988) The chlorophyll a/b-binding protein inserts into the thylakoids independent of its cognate transit peptide. J Biol Chem 263:14996-9
Lamppa, G K; Abad, M S (1987) Processing of a wheat light-harvesting chlorophyll a/b protein precursor by a soluble enzyme from higher plant chloroplasts. J Cell Biol 105:2641-8