Conjugates of biomolecules to nanoparticles
Disclosed herein are conjugates comprising a biomolecule linked to a label that have biological activity and are useful in a wide variety of biological applications. For example, provided herein are polymerase-nanoparticle conjugates including a polymerase linked to a nanoparticle, wherein the conjugate has polymerase activity. Such conjugates can exhibit reduced aggregation and improved stochiometries wherein the average biomolecule:nanoparticle ratio approaches or equals 1:1. Also disclosed herein are improved methods for preparing such conjugates, and methods and systems for using such conjugates in biological applications such as nucleotide incorporation, primer extension and single molecule sequencing.
1. A method for preparing a population of polymerase-nanoparticle conjugates which comprise a polymerase linked to a nanoparticle, where the polymerase includes a His-tag at the N-terminal end, and where the polymerase is linked to the nanoparticle via a His-tag mediated attachment, thereby forming a polymerase-nanoparticle conjugate, and where the conjugate has polymerase activity, wherein the polymerase-nanoparticle conjugate is prepared by:
a) producing a polymerase including a His-tag, and
b) contacting the polymerase with a nanoparticle and a quantity of an accessory compound under conditions where the polymerase becomes linked to the nanoparticle via a His-tag mediated attachment, thereby forming a a population of polymerase-nanoparticle conjugates with an average of about 0.5 to 1.5 polymerases per nanoparticle, wherein the accessory compound is selected from a group consisting of horseradish peroxidase, mucin, albumin, avidin, chloramphenicol acetyl-transferase, maltose binding protein and uracil DNA glycosylase or a combination thereof.
2. The method of claim 1 , wherein the resulting population of polymerase-nanoparticle conjugates comprises at least about 20% of the conjugates including an average of 1 polymerase per nanoparticle, relative to total number of nanoparticles in the population.
3. The method of claim 1 , wherein the nanoparticles comprise CdSe-ZnS core-shell nanoparticles.
4. The method of claim 1 , wherein the DNA polymerase comprises Phi29 DNA polymerase.
5. The method of claim 1 , wherein the plurality of nanoparticles is contacted in step (b) with histidine tagged uracil DNA glycosylase (UDG) and uracil DNA glycosylase inhibitor (ugi) to generate histidine tagged UDG-ugi conjugates.
6. The method of claim 5 , wherein the plurality of nanoparticles is contacted in step (b) with the histidine-tagged UDG-ugi conjugates in a 1:18 molar ratio of nanoparticles to histidine-tagged UDG-ugi conjugates.
7. The method of claim 5 , wherein the plurality of nanoparticles is contacted in step (b) with the histidine-tagged UDG-ugi conjugates in a 1:16 molar ratio nanoparticles to histidine-tagged UDG-ugi conjugates.
8. The method of claim 5 , wherein the plurality of histidine-tagged UDG-ugi nanoparticle conjugates in step (c) is contacted with the histidine-tagged DNA polymerases in a 1:4 molar ratio of histidine-tagged UDG-ugi nanoparticle conjugates to histidine-tagged DNA polymerases.
9. The method of claim 5 , wherein the plurality of histidine-tagged UDG-ugi nanoparticle conjugates in step (c) is contacted with the histidine-tagged DNA polymerases in a 1:2 molar ratio of histidine-tagged UDG-ugi nanoparticle conjugates to histidine-tagged DNA polymerases.
10. The method of claim 5 , wherein the plurality of histidine-tagged UDG-ugi nanoparticle conjugates in step (c) is contacted with the histidine-tagged DNA polymerases in a 1:1 molar ratio of histidine-tagged UDG-ugi nanoparticle conjugates to histidine-tagged DNA polymerases.