  Recently a technique based on the interaction between adhesion proteins
extracted from Streptococcus pyogenes, known as SpyRing, has been widely used
to improve the thermal resilience of enzymes, the assembly of biostructures,
cancer cell recognition and other fields. In SpyRing, the two termini of the
target enzyme are respectively linked to the peptide SpyTag and its protein
partner SpyCatcher. SpyTag spontaneously reacts with SpyCatcher to form an
isopeptide bond, with which the target enzyme forms a close ring structure. It
was believed that the covalent cyclization of protein skeleton caused by
SpyRing reduces the conformational entropy of biological structure and improves
its rigidity, thus improving the thermal resilience of the target enzyme.
However, the effects of SpyTag/ SpyCatcher interaction with this enzyme are
poorly understood, and their regulation of enzyme properties remains unclear.
Here, for simplicity, we took the single domain enzyme lichenase from Bacillus
subtilis 168 as an example, studied the interface interactions in the SpyRing
system by molecular dynamics simulations, and examined the effects of the
changes of electrostatic interaction and van der Waals interaction on the
thermal resilience of target enzyme. The simulations showed that the interface
between SpyTag/SpyCatcher and lichenase is different from that found by
geometric matching method and highlighted key mutations that affect the
intensity of interactions at the interface and might have effect on the thermal
resilience of the enzyme. Our calculations provided new insights into the
rational designs in the SpyRing.
