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LMM Biophysics 2

Light Microscopy Module Biophysics-2 (LMMBIO-2)

Research Overview

The main objective of Light Microscopy Module Biophysics-2 (LMMBIO-2) is to understand why protein crystallization experiments in microgravity have often generated unexpectedly low or high numbers of crystals. Both of these outcomes may negatively affect experiments designed to obtain a small number of well-separated crystals for x-ray structure studies.

This unpredictability has been associated with the suppression of buoyancy-driven convection. The conclusion is supported by data indicating the protein crystal nucleation reaches a maximum at an optimal convection velocity. Developing a better understanding of the effects of solution convection on crystal nucleation is a crucial issue in several fields of science and engineering. LMMBIO-2 also tests whether solution convection enhances or suppresses the formation of the dense liquid clusters, within which the crystal nuclei form.

These tests require characterization of the dense liquid clusters at different rates of convection, including its complete absence, and are only possible in microgravity. The Light Microscopy Module (LMM) aboard the International Space Station (ISS) is used to observe the formation of these clusters. Also, a newly-developed method, called differential dynamic microscopy, is used in order to quantify the dynamics of the dense liquid clusters. Variation in solution composition and the rate of convection are used to identify the cluster formation mechanisms.

Description

The main focus of Light Microscopy Module Biophysics-2 (LMMBIO-2) investigation is to better understand the effects of shear flow on nucleation precursors and therefore, on crystal nucleation. In a microgravity environment, nearly zero-flow states within homogeneous and phase-separating specimens can be maintained for long time periods, providing a baseline against which sheared fluids can be compared. This project is unusual in that the Research Team is also testing a fundamental hypothesis about proteins in solution; that, at moderate to high concentrations, (1) a very small fraction of the protein exists in a dense liquid phase in the form of Brownian particles, each a cluster of roughly 105 protein molecules undergoing liquid-like dynamics, and (2) crystal nucleation occurs when a small, ordered domain forms within the highly concentrated liquid-state environment of one of these particles.

The Research Team presented evidence from shear flow in a droplet that shear affects the precursors in such a way that crystal nucleation occurs most efficiently at a specific strain rate. The hypothesis is that shear leads to ordering by (a) creating local anisotropy within a dense liquid cluster, and (b) by changing the conformation of the protein so that nonpolar residues are exposed, and “hydrophobic” interactions are enhanced. Defining and characterizing dense liquid clusters has significant scientific merit, not only for the understanding and control of crystal nucleation, but also because low volume fraction dense liquid clusters may be universal in concentrated systems.

Science Objectives

The Light Microscopy Module Biophysics-2 (LMMBIO-2) investigation characterizes the behavior of dense liquid clusters at different rates of convection, utilizing differential dynamic microscopy. In microgravity, near-zero flow states can be maintained for long time periods, providing a baseline against which to compare sheared fluids. LMMBIO-2 also tests whether, at moderate to high concentrations, a fraction of a protein exists in a dense liquid phase, and whether crystal nucleation occurs when a small, ordered domain forms within the concentrated liquid-state environment of one of these particles.

Science Results

Find your best microscopic technique to observe tiny and changing physical phenomena aboard the International Space Station (ISS). Researchers have discovered that Differential Dynamic Microscopy (DDM) is a better approach than Dynamic Light Scattering (DLS) for examining small and large particles in dilute mixtures. DDM may be used in the future to measure the rate at which different physical phenomena changes, like the speed of sedimentation and diffusion.

Applications

Space Applications

Defining and characterizing dense liquid clusters is significant for the understanding and control of crystal nucleation. In addition, low volume fraction dense liquid clusters may be universal in concentrated systems. These processes can contribute to development of new materials for use in future spacecraft.

Earth Applications

Light Microscopy Module images provide data that help scientists and engineers understand the forces that control organization and dynamics of matter at microscopic scales. The organization and movement of matter on the microscopic level profoundly affects the macroscopic world and understanding such processes contributes to development of more efficient materials and machines for application on Earth and in space.

Publications

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