The Protein Streak Seeding Project

The goal of the Protein Streak Seeding project is the creation of an innovative high-throughput (HTP) microrobotic system for a protein crystallography task called streak seeding. The system uses visual feedback from a camera mounted on a microscope to control a micromanipulator which has the mounting tool attached as its end-effector. For use with our robotic system, we have developed unique new tools, called miscroshovels, which are designed to address certain limitations of the traditionally used by crystallographers whiskers, bristles, or other kinds of hair.

The motivation for this project, along with some background information, is described separately.

Streak seeding is useful when the initial crystallization experiments yield crystals which are too small (less than 40um in size) and/or of low quality and can not be used for structure determination. To obtain higher quality crystals, a new reaction is setup like the original one, however, before incubation, small fragments of the initially obtained crystals are transferred to the new protein-reagent mixture to bootstrap the crystallization process. This crystal fragment transfer process is called streak seeding.

The task of streak seeding consists of three steps (right). First, the tool to be used is washed in clean water to remove any residue. Second, the tool is used to touch and probe the existing crystals thus breaking them up into fragments and picking some up. Third, the tool is streaked through the fresh mixture, which deposits some of the fragments in it. For this to work, the tool has to have the necessary properties to be able to break up, retain and release crystal fragments. Typically, various types of hair, bristles, whiskers or horse tail are used.

We have designed and assembled a micro-robotic system for protein crystal manipulation, which we use for our research and experiments. The system uses our own custom tools, called microshovels, which we designed and fabricated using MEMS technology.

The streak seeding system is designed to work with the hanging drop crystallization method, seeding from source crystals on a 22mm square coverslip to destination drops on a coversheet for a 96-well plate. The user sets up the system by placing on the stage the coverslip with the protein crystals, the coversheet of the 96-well plate with the target protein droplets, and a microbridge with water used for cleaning the seeding tool. Then the system is started and it performs the seeding autonomously. The video on the right (sped up twice) shows the system in operation.