Designed by: Charles Gleason   Group: iGEM16_Stanford-Brown   (2016-09-07)

Bacterial Collagen with Elastin Cross-linker and Homotrimeric Coiled-Coil Domain

See the design page or the relevant wiki[1] for more details.

Sequence and Features

Assembly Compatibility:
  • 10
  • 12
  • 21
  • 23
  • 25
  • 1000
    Illegal SapI.rc site found at 70
    Illegal SapI site found at 175


After induction of our liquid cultures, we extracted the proteins from our constructs. We kept all protein washes to assure that our desired protein product did not get extracted earlier than expected (we expected the protein to be in the final elution buffer washes). After confirming its presence in the final elution washes (shown below), we ran the extracts against each other. To verify the size of the protein, we ran our protein extractions in SDS-PAGE gels. We mostly used Ni columns to purify our protein extract. Since our construct has a Lumio-Flag-His tag, we also used Anti-FLAG magnetic beads, with the help of our mentor Kosuke, to examine which protocol was most efficient in extracting protein.


SDS-PAGE gel of all washes of extracted proteins using Ni-NTA resin columns and Lumio staining. AF stands for Anti-FLAG, and represents samples that were extracted using Anti-FLAG magnetic beads

SDS-PAGE gel of extracted C2 and CN proteins (lanes 2-5 and lanes 6-8 respectively) using Lumio stain. Lanes 2-5 represent the Lumio stained protein extract of the BioBrick Part:BBa_K2027005 or construct 2 (C2). Lanes 2,3, and 4 are respectively first, second, and third elution buffer washes using the His-tag nickel resin columns. Lane 5 is also C2's extracted protein, however it was extracted using a different protocol, Anti-FLAG. Lanes 6-8 contains corresponding elution buffers of the natural construct (CN), Part:BBa_K2027007. CN was extracted using His-tag nickel resin columns.

We also explored the possibility of cross-linking the proteins. Our plan was to cross-link the proteins and compare the results with un-processed protein in an SDS-PAGE. Initially, we wanted to test small samples of cross-linked C1, C2, and C3 and S1, S2, and S3 against non-cross-linked samples. We expected cross-linked proteins to have a higher molecular weight than proteins that weren't. Since this was our first time attempting to cross-link proteins, we wanted to test our protocol on only one sample before proceeding on a large-scale cross-linking experiment.

In this experiment, we used pure pyrroloquinoline quinone (PQQ) as a catalyst for the cross-linking reaction for sample construct CN. PQQ was diluted in a copper (II) solution and mixed with the purified protein. Since the purified protein exists in a phosphate buffer (extract was purified from the Ni-NTA resin columns), we maintained the pH of the reaction solution and kept it close to pH 7 while adding excess copper because the precipitation of copper(II) phosphate causes an increase in acidity of the buffer. When the solution became basic, we found that the solution was mostly clear and the precipitate was a light green-blue color, likely copper hydroxide. When the solution was nearly pH 7 and borderline acidic, the solution turned a clear blue and produced a fine blue copper(II) phosphate precipitate, but copper remained in solution. We incubated the two different sample solutions at room temperature for 24 hours. After 24 hours, we found that the solutions separated into two layers. We weren't sure if the cross-linked protein would exist in the precipitate-like layer or the supernatant so we ran both against the original untreated CN in a gel.

T--Stanford-Brown--crosslinkingsolutions.jpeg Tubes containing the cross-linking reaction solution. Left tube is pH 8 and right tube is pH is 6.8.

T--Stanford-Brown--xlink_pagegel.jpeg SDS-PAGE with Lumio stain of non-cross-linked and cross-linked CN protein. Lane 2 is the untreated CN protein. Lanes 3 and 4 are the pH 6.8 tube's precipitate and supernatant, respectively. Lanes 5 and 6 are the pH 8 tube's precipitate and supernatant, respectively.

The SDS-PAGE gel results showed that cross-linking did not occur. It is difficult to read the gel because the protein may have run off early on. In this experiment, we used a different gel percentage, 8%, because we ran out of our usual gel type. This is the third iteration of running our SDS-PAGE gel, because we had trouble figuring out the optimal run conditions. Even though the gel was run at 200 V for 10 minutes, the samples were mostly at the bottom. This may have contributed to the production of a messy gel. Due to time constraints and material limitations, we could not rerun more gels to further optimize our protocol. Despite the difficulty in gauging the exact results of the gel, we estimated our results of failure based on the location of the untreated CN band. The bands in the other lanes were approximately around the same location, suggesting that the treated proteins did not change in size. We found it peculiar that the lanes 3 and 4 had additional bands of smaller molecular weight and are unsure what it is.