Purification Experiment Set-Up

Last Friday (October 25th), JP introduced me to another project that our lab is working on. Previously, we had two different ways to produce free peptide. First, we could grow peptides off cellulose and dissolve the cellulose in DMSO to leave the free pepide in solution. Second, we could grow peptides off of a polymer bead that has  functional groups for the peptide to attach to. These linkers could then be cut using a strong acid to produce free peptide. Now, we are working on producing peptide that grows directly off of the polymer bead, so it cannot be cleaved. Using these beads in a column, we could purify biologic. When biologic is entered into the top of the column, it would be captured by the column through the peptides. We could then elute off the biologic.

To prep for this experiment, I inserted seven specific amino acid sequences into the peptide machine program, copying each 13 times. After inserting the sequences, I used the program to see what volume of each amino acid prepped amino acids for the peptide machine. I then rounded those values up to either 5, 10, or 15 mL of solution. After determining the amount of each solution we would need, I calculated the gram amount of amino acid and mL amount of NMT to be added to make each solution. I then labeled each amino acid tube and added the specified grams of amino acid to each.

We will use the amino acid solutions that I made today to produce the seven specified peptides that I entered into the program. I look forward to returning to RPI next Friday to see what progress has been made!

HCP Assay

On Friday (October 11th), I had a variety of different tasks at RPI. My main task was to help Doug with an host cell protein (HCP) assay. In this experiment, we plan to analyze the binding of HCP to a peptide array using high-thoroughput screening of fluorescent tags. To do so, the peptide arrays will be incubated with HCP solution, primary antibody, and secondary antibody, separated by thorough washings to remove the excess solution. We will be testing different concentrations of primary antibody. The secondary antibody is fluorescently tagged, so we can screen the slides for intensity, indicating the intensity of HCP bound by each peptide.

Figure by JP Trasatti, Karande Lab, RPI

Previously, Doug printed peptides arrays onto three different slides and coated them with an HCP solution to bind the peptides. My first job was to wash the HCP solution off of the slides. This washing involves pouring off the solution from the slide and adding 10 mL of PBS to the petri dish, then rotating them for 10 minutes to wash off any excess HCP that was not bound by the peptide array. We then made the different concentrations of primary antibody and applied them to the respective slides, making sure all of the solution stayed on the slide and was evenly distributed. After an hour of incubation, we then washed the primary antibody and applied the light-sensitive secondary antibody.

While we were waiting for the primary antibody incubation, we were going to make western transfer buffer, but we did not have enough methanol. Instead, we made 2L of PBS, which is a process I have done before!

I am excited to return to RPI and see the results of this experiment, but I will unfortunately not be able to go this Friday (October 18th) due to Parents' Day.

Host Cell Proteins

On Friday (October 4th), I finally returned to RPI after missing a week! I worked with Doug (one of the undergraduates in my lab) on a project he is working on involving host cell proteins. A couple weeks ago, these host cell proteins were involved in the SDS-PAGE gel we were working on!

Previously, we have only had intensity data to analyze the amount of host cell protein (HCP) that is bound by different peptides. This is relative data, so it does not give us information about the actual amount of HCP that binds. Ideally, we want to find a peptide that has a high affinity for the target protein we are looking to purify, but low intensity of HCP (the green square in the graph below). We do not want the result to be in the red square, indicating high affinity for the target protein, but high intensity of HCP.

Doug is working to quantify the amount of HCP that is bound by the peptides. To do so, he is printing different concentrations of HCP on nitrocellulose (negatively charged paper) 3X5 microarrays. These spots of known HCP amount will then be analyzed for intensity to determine a standard curve. The standard curve will then be used to determine the unknown (amount of HCP) for the peptide data.

My first job was to pipette 80 microliters of 6 different concentrations of HCP into their specified positions in the printer well-plate. We then cut the nitrocellulose paper into slide-shaped pieces and taped them onto the printer so they wouldn't move during printing. When we were setting the heights for the printer needle, one of the pieces of nitrocellulose cracked, so we had to untape and redo the nitrocellulose. Once we finally had the printer set up, we set the first round of printing to run, and we found that the middle spot on the second slide was not printing. We then reconfigured the needle heights and made each height tighter to the nitrocellulose. As we continued to run the machine, we realized that the needle was popping up every time it went to print on the first slide, so we had to tap the needle down every time it was positioned on the first slide. Because the printing was taking so long, we decided to only do 10 runs instead of the original 20 runs planned. Even the 10 runs took over 2 hours to complete!

I look forward to returning to RPI next week to see what data they collected from this experiment!