Part:BBa_K4765016

Hypsibius exemplaris mitochondrial single-stranded DNA binding protein (H. ex mtSSB)

Introduction

H. ex mtSSB is a type of mitochondrial single-stranded DNA binding protein derived from Hypsibius exemplaris . H. ex mtSSB is non-specific in binding single-stranded DNA. ssDNA is exposed by normal cellular functions like replication and transcription, as well as during genotoxic stress. DNA wrapped around H. ex mtSSB could be physically buffered against DNA damage and ensuing lethality. Under harsh conditions like desiccation heat, and radiation, H. ex mtSSB can maintain the stability of DNA through the above mentioned mechanism, thus enhance the survival rate of organisms in harsh environments.

Usage and Biology

We heterologously expressed H. ex mtSSB in E. coli, conferring improved resistance to desiccation and UV radiation. We also compared its desiccation resistance with that of SAHS 33020(BBa_K2306003) and tested the combined desiccation resistance of both proteins in BBa_K4765117

Characterization

Sequencing map

Figure 1. Sequencing map of H. ex mtSSB Sequencing starts from the T7 terminator, with the primer 5-GCTAGTTATTGCTCAGCGG-3.

Desiccation Survival Assay

We attempt to compare the anti-desiccation capabilities of H. ex mtSSB and the pre-existing protein SAHS 33020BBa_K2306003 in order to identify a suitable desiccation-resistant protein for B-HOME. Through the experiments, we found that H. ex mtSSB exhibits desiccation resistance comparable to SAHS.

Figure 2. Workflow of Desiccation Survival Assay

We've designed an experimental group with H. ex mtSSB and SAHS 33020, and used E. coli transformed with the empty PET28 vector as a control. All proteins are expressed via leakage in E. coli BL21 DE3. All the groups are incubated overnight. After reaching an OD value of 1.0, liquid culture is centrifuged, and the supernatant is removed. Pellets are dried for 6.5 hr in SpeedVac (Savant SpeedVac SC100) under 4 0 °C .Finally, the pellets are resuspended in LB medium and dilute 10^5-fold for CFU counting.

Figure 3. Dry weight of H.ex mtSSB, TDP, and control after drying There is no statistically significant difference in the dry weights among the experimental groups, indicating that the number of E. coli is consistent between the bacterial tubes.

Figure 3. CFU colony count of H.ex mtSSB, TDP, and control after drying Colonies (CFU/mL)= CFU count*10^6= CFU count*10^6 The E. coli expressing H.ex mtSSB and SAHS showed higher CFU counts after drying compared to the control group, indicating their desiccation resistance abilities.

Anti-UV Survival Assay

We employed the Colony-Forming Unit (CFU) assay. After plasmid transformation and plating, we shielded one/half of the agar plate from UV light using a black cloth, while the other one/half was exposed to UV irradiation (6W power) with wavelengths of 254 nm and 365 nm for 10 seconds.

Figure 2. Anti-UV Assay.

In our experimental findings, while mtSSB effectively guards against DNA damage caused by desiccation through its binding to single-stranded DNA, we did not observe any enhancement in UV resistance in E. coli expressing mtSSB. Surprisingly, the survival rate of E. coli expressing mtSSB was even lower than that of the control group without mtSSB.

Figure 3. Survival Rate after UV Exposure. Percentage of viable E. coli expressing proteins following UV radiation exposure (Note: The quantitative graph is based on the whole plate CFU to avoid the blurriness at the boundaries of the cloth-shielded area from UV.)

Sequence and Features

Assembly Compatibility:

• 10
  COMPATIBLE WITH RFC[10]
• 12
  COMPATIBLE WITH RFC[12]
• 21
  COMPATIBLE WITH RFC[21]
• 23
  COMPATIBLE WITH RFC[23]
• 25
  INCOMPATIBLE WITH RFC[25]

  Illegal NgoMIV site found at 186
  
• 1000
  INCOMPATIBLE WITH RFC[1000]

  Illegal BsaI.rc site found at 454
  Illegal BsaI.rc site found at 535
  Illegal SapI site found at 348