Characterization and inhibition of the CaaX processing prelamin A protease ZMPSTE24
Abstract
CaaX processing is a crucial post-translational processing event that occurs in three obligatorily sequential steps to proteins that have a CaaX sequence at the carboxyl terminus, where C is a cysteine, A is generally an aliphatic amino acid, and X is one of several amino acids. First, the cysteine is prenylated with either a farnesyl or geranylgeranyl moiety. Second, the aaX amino acids are removed by one of two endoproteases, RCE1 or ZMPSTE24. Finally, the newly exposed farnesylcysteine carboxylate is methylated by an isoprenylcysteine carboxylmethyltransferase (ICMT). The proteins that undergo this series of posttranslational modifications play many roles within the cell, including proteins involved in signal transduction and proteins crucial to the proper structure of organelles. ZMPSTE24, one of the two CaaX processing proteases, has only one known substrate, prelamin A. Not only does ZMPSTE24 cleave prelamin A at its CaaX box, but ZMPSTE24 also catalyzes an upstream cleavage event that is the final step in the maturation of prelamin A. Mature lamin A is a component of the nuclear lamina, which provides structure to the nuclear envelope. Mutations of either the gene coding for prelamin A or ZMPSTE24 have been implicated in several diseases, including Hutchinson-Gilford Progeria Syndrome (HGPS), mandibuloacral dysplasia (MAD), restrictive dermopathy (RD), and lipodystrophy. HGPS is the result of a splice site mutation that removes the second ZMPSTE24 cleavage site in prelamin A. As a result, farnesyl-prelamin A accumulates in the nucleus, which is toxic to the cell. MAD and RD have been found to be the result of mutations in ZMPSTE24. Several missense mutations of ZMPSTE24 have been identified in MAD that are heterozygous with a truncation mutant. RD, a lethal fetal syndrome, is the result of ZMPSTE24 truncation mutations. Familial partial lipodystrophy has been found to be the result of mutations in the gene that encodes for prelamin A, but a common side effect of HIV pharmaceuticals is lipodystrophy. It has been found that several HIV protease inhibitors also inhibit the proteolytic activity of ZMPSTE24. The work presented in this thesis investigates the biochemistry of ZMPSTE24 in these various diseases.^
Degree
Ph.D.
Advisors
Christine A. Hrycyna, Purdue University.
Subject Area
Chemistry, Biochemistry
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