Hi.
I’m a student who is just starting out in lab . I’ve got some doubts to clear. Hope anybody cann help me.
I’m currently trying to purify a protein whose protein expression level is rather low. But the instructions I got from my sup isn’t very clear and I would like try and optimize the condition for protein production without having to increase the volume.
I read in one of the topic that IPTG induction is carried for no more than 5 hours. But what I was doing is to leave it overnight, usually for 18hrs. Is it too long? or shall I vary the concentration of IPTG to find the optimal value, how long incubation time could you suggest?
Does the time of induction affect protein production? I was taught that if you are working with small volume, it is alright to directly add IPTG right from start. But for large scale, it is to be added when the OD reaches around 0.7. Could someone explain to me?
As my protein of interest has a His-tag, will the incubation time with nickel beads be a factor worth considering and how about the amount of nickel beads added?
If you’re observing good protein expression after 5 hours, it’s best to stick to this duration. However, you can optimize this by experimenting with shorter times, such as 3 or 4 hours, to see if the protein yields are similar or better.
Start with standard concentrations like 0.1 mM to 1 mM and try different time points (e.g., 3-5 hours) to optimize both the concentration and time of induction.
OD at Induction (0.6-0.8): At this point, the bacteria are actively dividing and have the energy reserves to take up and process IPTG, maximizing protein expression without overwhelming the cells.
For large-scale cultures, let the OD reach 0.6-0.8 before adding IPTG to ensure efficient protein expression and minimize stress.
The length of time the lysate is incubated with the nickel beads for His-tag affinity purification can indeed impact the yield and efficiency of protein binding. In general, 30 minutes to 1 hour is sufficient for most applications. If you leave it for too long, there’s a possibility of non-specific binding, though His-tagged proteins usually bind quite well within a shorter timeframe.
A general rule of the thumb is to use about 0.1–0.2 mL of packed beads per 10-20 mg of protein. You can scale this depending on the total protein and volume you’re purifying.