This gene encoded a mitochondrial matrix protein that is the subunit of a barrel-shaped homo-oligometric protein complex, the Lon protease. Lon protease is a member of ATP-dependent proteases (AAA+ proteases). Mature and catalytically viable Human Lon protease complex contains a hexameric ring while other formations of complexes have been observed (e.g., heptameric ring in Saccharomyces cerevisiae). A single subunit of Lon protease contains three domains, N-Domain for protein substrate recognition, AAA + module for ATP binding and hydrolysis, and P-domain for protein proteolysis. A similar protease expressed in E. coli regulates gene expression by targeting specific regulatory proteins for degradation. Lon protease binds a specific sequence in the light and heavy chain promoters of the mitochondrial genome which are involved in regulation of DNA replication and transcription.
Lon protease (LONP1) is a conserved serine peptidase identified from bacteria to eukaryotic cells. In mitochondrial matrix, a majority of damaged proteins is removed via proteolysis led by Lon protease, which is an essential mechanism for mitochondrial protein quality control (PQC).
For Lon protease-dependent degradation, protein substrates are first recognized and then unfolded if necessary in an ATP-dependent manner. The substrates are subsequently transferred through the pore of complex and into the proteolytic chamber of complex for degradation. ATP binding to the AAA module of the Lon complex results in a change in Lon conformation into a proteolytically active state. In general, Lon protease interacts with peptide regions(sequences) that are located within the hydrophobic core of substrates and rarely on the surface. These regions can be presented to Lon protease when proteins are damaged and lost their conformation integrity. In addition to misfolded proteins, several regulatory proteins can be processed by Lon protease by removing a degradable tag before they fully gain their biological functions.
LONP1 is also a DNA-binding protein that participates in mtDNA maintenance and gene expression regulation. LONP1 degrades mitochondrial transcription factor A (TFAM) when substrate is modified by post-translational modifications (PTMs) such as phosphorylation, regulating mtDNA copy number and metabolism to maintain the TFAM/mtDNA ratio necessary to control replication and transcription.
Given the crucial role of LON protease in maintaining the control of mitochondrial function, its dynamics in expression under stress conditions has been found associating with human diseases and aging. For example, LONP1 expression levels are increased in different tumors and tumor cell lines. Interestingly, downregulation of LONP1 in some tumor cells causes apoptosis and cell death, indicating a possible addiction of tumor cells to LONP1 function, as occurs with other intracellular proteases associated with cancer.
^Pinti M, Gibellini L, Liu Y, Xu S, Lu B, Cossarizza A (December 2015). "Mitochondrial Lon protease at the crossroads of oxidative stress, ageing and cancer". Cellular and Molecular Life Sciences72 (24): 4807–24. doi:10.1007/s00018-015-2039-3. PMID26363553.
^Lu B, Liu T, Crosby JA, Thomas-Wohlever J, Lee I, Suzuki CK (March 2003). "The ATP-dependent Lon protease of Mus musculus is a DNA-binding protein that is functionally conserved between yeast and mammals". Gene306: 45–55. doi:10.1016/s0378-1119(03)00403-7. PMID12657466.
^Birghan C, Mundt E, Gorbalenya AE (January 2000). "A non-canonical lon proteinase lacking the ATPase domain employs the ser-Lys catalytic dyad to exercise broad control over the life cycle of a double-stranded RNA virus". The EMBO Journal19 (1): 114–23. doi:10.1093/emboj/19.1.114. PMID10619850.
^Liu T, Lu B, Lee I, Ondrovicová G, Kutejová E, Suzuki CK (April 2004). "DNA and RNA binding by the mitochondrial lon protease is regulated by nucleotide and protein substrate". The Journal of Biological Chemistry279 (14): 13902–10. doi:10.1074/jbc.m309642200. PMID14739292.
^Lu B, Lee J, Nie X, Li M, Morozov YI, Venkatesh S, Bogenhagen DF, Temiakov D, Suzuki CK (January 2013). "Phosphorylation of human TFAM in mitochondria impairs DNA binding and promotes degradation by the AAA+ Lon protease". Molecular Cell49 (1): 121–32. doi:10.1016/j.molcel.2012.10.023. PMID23201127.
^Ngo JK, Pomatto LC, Davies KJ (9 February 2013). "Upregulation of the mitochondrial Lon Protease allows adaptation to acute oxidative stress but dysregulation is associated with chronic stress, disease, and aging". Redox Biology1: 258–64. doi:10.1016/j.redox.2013.01.015. PMID24024159.
^Hamon MP, Bulteau AL, Friguet B (September 2015). "Mitochondrial proteases and protein quality control in ageing and longevity". Ageing Research Reviews23 (Pt A): 56–66. doi:10.1016/j.arr.2014.12.010. PMID25578288.
Lu B, Yadav S, Shah PG, Liu T, Tian B, Pukszta S, Villaluna N, Kutejová E, Newlon CS, Santos JH, Suzuki CK (June 2007). "Roles for the human ATP-dependent Lon protease in mitochondrial DNA maintenance". The Journal of Biological Chemistry282 (24): 17363–74. doi:10.1074/jbc.M611540200. PMID17420247.
Bota DA, Ngo JK, Davies KJ (March 2005). "Downregulation of the human Lon protease impairs mitochondrial structure and function and causes cell death". Free Radical Biology & Medicine38 (5): 665–77. doi:10.1016/j.freeradbiomed.2004.11.017. PMID15683722.
Liu T, Lu B, Lee I, Ondrovicová G, Kutejová E, Suzuki CK (April 2004). "DNA and RNA binding by the mitochondrial lon protease is regulated by nucleotide and protein substrate". The Journal of Biological Chemistry279 (14): 13902–10. doi:10.1074/jbc.M309642200. PMID14739292.
Lu B, Liu T, Crosby JA, Thomas-Wohlever J, Lee I, Suzuki CK (March 2003). "The ATP-dependent Lon protease of Mus musculus is a DNA-binding protein that is functionally conserved between yeast and mammals". Gene306: 45–55. doi:10.1016/S0378-1119(03)00403-7. PMID12657466.
Bota DA, Davies KJ (September 2002). "Lon protease preferentially degrades oxidized mitochondrial aconitase by an ATP-stimulated mechanism". Nature Cell Biology4 (9): 674–80. doi:10.1038/ncb836. PMID12198491.
Fu GK, Markovitz DM (February 1998). "The human LON protease binds to mitochondrial promoters in a single-stranded, site-specific, strand-specific manner". Biochemistry37 (7): 1905–9. doi:10.1021/bi970928c. PMID9485316.