Super-Resolution Fluorescence Imaging of Spatial Organization of Proteins and Lipids in Natural Rubber

Abstract

Natural rubber (NR) with proteins and lipids has superior mechanical properties to its synthetic counterpart, polyisoprene rubber. However, it is a challenge to unravel the morphology of proteins and lipids. Here we used two-color stochastic optical reconstruction microscopy (STORM) to directly visualize the spatial organization of proteins and lipids in NR. We found that the proteins and lipids form an interdispersed stabilizing layer on the surface of NR latex particles. After drying, the proteins and lipids form aggregates of up to 300 nm in diameter. The aggregates physically interact with the terminal groups of polyisoprene chains, leading to the formation of a network, which contributes to the high elasticity and mechanical property of NR. If we remove proteins in NR, the large phospholipid aggregates disintegrate into small ones. However, it does not decompose the network but rather reduces the effective cross-linking density, thus the deproteinized NR is still elastic-like with decreased mechanical property. Removing both proteins and lipids wholly decomposes the network, thus, results in a liquid-like behavior of the rubber. The STORM measurements in this paper enable more insight into the structure-property relationship of NR, which also shows a great potential of STORM in studying the fine structure of polymeric materials and nanocomposites.

Effect of protein on the thermogenesis performance of natural rubber matrix

“…So we can infer that when stress is loading, the preferential break of the protein network will absorb part of the energy to reduce heat generation. Moreover, the protein free in the NR matrix similar to filler will attach to the polyisoprene chain in the form of entanglement-like 22 , 34 , 35 . We have been proven that entanglement restricts the movement of molecular chains thus reduces heat generation 7 .…”

“…The mass proportion of protein in NR is about 1.5–4 m%, which is the most representative of non-rubber components 22 . Our research found that proteins and phospholipids act as sacrificial network in the NR matrix, thus enhance the network structure toughness and strength 23 , 24 .…”

A Review on Characterization of Molecular Structure of Natural Rubber

“…It demonstrated that branch-points of NR molecular chain have been decomposed after purifying. According to the states above, it is remarkable that the ω-terminal associated with protein and α-terminal associated with phospholipids form network in NR by hydrogen bonding or some metal ions, 16,[26][27][28] as showed in Figure 2. In addition to, there are abnormal groups including epoxide group, hydroxyl, aldehyde groups, carboxyl groups and 3, 4-isoprene on NR molecular chain.…”

“…15 Recently the spatial organization of proteins and lipids in NR can be directly visualized by two-color stochastic optical reconstruction microscopy (STORM), which providing an advanced analysis method to study structure of NR latex particles. 16 However, these approaches are demanding, require chemical fixation and airdrying, and do not provide original morphology of NR latex particles.…”

Pre‐Vulcanization of Large and Small Natural Rubber Latex Particles: Film‐Forming Behavior and Mechanical Properties

“…NR latex particles in the range of nano to micron size are naturally biosynthesized and accumulated as spherical structure with hydrophobic polyisoprene core, surrounded by a protein and phospholipid mixed monolayer (ca. 4 nm thick) in a shell structure . In freshly tapped latex from Hevea rubber tree, RPs show a wide range of particle size (φ), varying from 30 nm to a few microns which are typically classified into large (φ > 250 nm) and small rubber particles (φ < 250 nm), designated as LRP and SRP, respectively .…”