Sandbox Reserved 191: Difference between revisions

'''<scene name='43/436866/Overall-3-rainbow/1'>PPT-1</scene>''' is a lysosomal enzyme, which has a serine [[lipase]] consensus sequence; a key characteristic of lysosomal enzymes. Despite having a serine lipase consensus sequence, PPT-1, is not deactivated by phenylmethylsulfonyl fluoride [https://en.wikipedia.org/wiki/PMSF (PMSF)], a common serine-modifying reagent. <scene name='58/580839/Hdsf_by_itself/1'>Hexadecylsulfonylfluoride</scene>  (HDSF) is a serine-modifying reagent that is able to <scene name='58/580839/Basic-hdsf-nosurface/4'> bind and inhibit PPT-1</scene>. Unlike other inhibitors, <scene name='58/580839/Basic-hdsf-surfacelook/2'>HDSF is able to fit in the narrow, hydrophobic groove of PPT-1</scene> leading away from the active site of PPT-1. PMSF is unable to fit into this small narrow groove due to steric constraints that relate to the unique structure of the substrate-binding site of PPT-1.  The sulphur of HDSF will <scene name='58/580839/Hdsf_bound_to_ser-115-best/1'>bind to SER-115 in the active site of PPT-1</scene> via a sulponylation reaction and thus will inhibit the actions of PPT-1<ref name="INCL">PMID:10801859</ref>

[[Image:All_mutations.jpg|200px|right|thumb|Figure 3: Mutations to PPT-1 associated with INCL.  Twelve common mutations of INCL are shown in the white on the blue PPT-1 protein.]]

[https://en.wikipedia.org/wiki/Infantile_neuronal_ceroid_lipofuscinosis Infantile neuronal ceroid lipofuscinosis (INCL)] is a recessively inherited disease that is associated with a decrease in PPT-1 activity due to mutations in PPT-1. Onset of symptoms which include retinal blindness, ataxia, seizures, and cortical atrophy of the brain, begin 1-2 years after birth. Death typically occurs between the ages of 8-11. Several mutations in the ''1p32'' chromosome have been identified to cause INCL <ref name="mutations" />.

Juvenile NCL (JNCL) and Late-Infantile NCL (LINCL) are less severe forms of INCL in which onset of symptoms occur much later in life; between the ages of 30-40. A possible explanation for the later onset of symptoms could be that the mutations associated with JNCL and LINCL occur away from the active site of PPT-1. Since the mutation does not affect the active site this results in a higher activity of the PPT-1 enzyme. A common mutation associated with JNCL and LINCL involves the mutation of Thr-75, an amino acid located on the alpha-1 helix of PPT-1 (Figure 4). The Thr-75 amino acid is located 20.6Å away from the active site of PPT-1 which indicates that Thr-75 plays no role in the catalytic activity of the catalytic triad  

<ref name="mutations" />.

In both JNCL and LINCL, the activity of PPT-1 has only a 2% activity rate compared to normal PPT-1 activity. This suggests that a small increase in activity of PPT-1 may aid in delaying the symptoms associated with INCL. One way to potentially increase the activity of mutant PPT-1 variants is to use [https://en.wikipedia.org/wiki/Protein_chaperones protein chaperones] that help refold PPT-1 in the [http://en.wikipedia.org/wiki/Endoplasmic_reticulum endoplasmic reticulum].  Although this is not a cure for INCL, increasing the activity of PPT-1 by only '''ABC'''-fold can also increase the life expectancy for individuals with INCL <ref name="Kelly-1">PMID:20346914</ref>.

Despite the life-threatening diseases associated with decreased PPT-1 activity, inhibition of PPT-1 has also been shown to be a potential cancer target. Proteins involved in signaling and growth are post-translationally modified with palmitic acid. PPT-1 is involved with removing palmitate from lipid-modified proteins and this [http://en.wikipedia.org/wiki/Palmitoylation palmitoylation] is necessary for membrane association. When PPT-1 is over expressed, cells become protected from cell death, which leads to tumor formation.  PPT-1 inhibition in cultured tumor cells led to selective tumor cell death. <ref name="Kelly-1" />