Part:BBa_K2619011

HSP70/Heat shock protein 70 (Homo sapiens)

Heat shock protein 70 (HSP70) is a chaperone that facilitates the degradation progress of aggregated synaptic proteins and alleviate symptoms caused by Lewy body and Lewy neurites, which are characteristic symptoms of many neurondegenerative disorders, including Parkinson’s disease(PD) (Ebrahimi-Fakhari et al., 2011). Our strategy makes use of exosomes to transport mRNA of HSP70 directly into target neurons to alter early pathological changes in proteinopathies such as PD.

The Hsp70 protein has three major functional domains:

1. N-terminal ATPase domain – binds ATP (Adenosine triphosphate) and hydrolyzes it to ADP (Adenosine diphosphate). The NBD (nucleotide binding domain) consists of two lobes with a deep cleft between them, at the bottom of which nucleotide (ATP and ADP) binds. The exchange of ATP and ADP leads to conformational changes in the other two domains.

2. Substrate binding domain – is composed of a 15 kDa β sheet subdomain and a 10 kDa helical subdomain. The β sheet subdomain consists of stranded β sheets with upward protruding loops, as a typical β barrel, which enclose the peptide backbone of the substrate. SBD contains a groove with an affinity for neutral, hydrophobic amino acid residues. The groove is long enough to interact with peptides up to seven residues in length.

3. C-terminal domain – rich in alpha helical structure acts as a 'lid' for the substrate binding domain. The helical subdomain consists of five helices, with two helices packed against two sides of the β sheet subdomain, stabilizing the inner structure. In addition, one of the helix forms a salt bridge and several hydrogen bonds to the outer Loops, thereby closing the substrate-binding pocket like a lid. Three helices in this domain form another hydrophobic core which may be stabilization of the "lid". When an Hsp70 protein is ATP bound, the lid is open and peptides bind and release relatively rapidly. When Hsp70 proteins are ADP bound, the lid is closed, and peptides are tightly bound to the substrate binding domain.

As newly synthesized proteins emerge from the ribosomes, the substrate binding domain of Hsp70 recognizes sequences of hydrophobic amino acid residues, and interacts with them. The presence of a peptide in the binding domain stimulates the ATPase activity of Hsp70, increasing its normally slow rate of ATP hydrolysis. When ATP is hydrolyzed to ADP the binding pocket of Hsp70 closes, tightly binding the now-trapped peptide chain. By binding tightly to partially synthesized peptide sequences (incomplete proteins), Hsp70 prevents them from aggregating and being rendered nonfunctional. Once the entire protein is synthesized, a nucleotide exchange factor stimulates the release of ADP and binding of fresh ATP, opening the binding pocket. The protein is then free to fold on its own, or to be transferred to other chaperones for further processing.

Hsp70 seems to be able to participate in disposal of damaged or defective proteins. Interaction with CHIP (Carboxyl-terminus of Hsp70 Interacting Protein)–an E3 ubiquitin ligase–allows Hsp70 to pass proteins to the cell's ubiquitination and proteolysis pathways.

Sequence and Features

Assembly Compatibility:

• 10
  COMPATIBLE WITH RFC[10]
• 12
  COMPATIBLE WITH RFC[12]
• 21
  INCOMPATIBLE WITH RFC[21]

  Illegal BglII site found at 362
  Illegal BglII site found at 1286
  
• 23
  COMPATIBLE WITH RFC[23]
• 25
  INCOMPATIBLE WITH RFC[25]

  Illegal NgoMIV site found at 447
  
• 1000
  INCOMPATIBLE WITH RFC[1000]

  Illegal BsaI.rc site found at 337
  Illegal SapI.rc site found at 1656