Structures of a FtsZ single protofilament and a double-helical tube in complex with a monobody

Engineering a monobody specific to monomeric Cu/Zn-superoxide dismutase associated with amyotrophic lateral sclerosis

Misfolding of mutant Cu/Zn-superoxide dismutase (SOD1) has been implicated in familial form of amyotrophic lateral sclerosis (ALS). A natively folded SOD1 forms a tight homodimer, and the dimer dissociation has been proposed to trigger the oligomerization/aggregation of SOD1. Besides increasing demand for probes allowing the detection of monomerized forms of SOD1 in various applications, the development of probes has been limited to conventional antibodies. Here, we have developed Mb(S4) monobody, a small synthetic binding protein based on the fibronectin type III scaffold, that recognizes a monomeric but not dimeric form of SOD1 by performing combinatorial library selections using phage and yeast-surface display methods. Although Mb(S4) was characterized by its excellent selectivity to the monomeric conformation of SOD1, the monomeric SOD1/Mb(S4) complex was not so stable (apparent Kd ~ μM) as to be detected in conventional pull-down experiments. Instead, the complex of Mb(S4) with monomeric but not dimeric SOD1 was successfully trapped by proximity-enabled chemical crosslinking even when reacted in the cell lysates. We thus anticipate that Mb(S4) binding followed by chemical crosslinking would be a useful strategy for in vitro and also ex vivo detection of the monomeric SOD1 proteins.

Streptothricin-F Inhibition of FtsZ Function: A Promising Approach for Controlling Pseudomonas syringae pv. actinidiae

Pseudomonas syringae pv. actinidiae (Psa) is a significant pathogenic bacterium affecting the kiwifruit industry. This study investigated the target sites of streptothricin-F (ST-F), produced by Streptomyces lavendulae gCLA4. The inhibition of ST-F on Psa was examined by the microscopic structural differences of Psa before and after treatment with ST-F, as well as the interaction between ST-F and cell division-related proteins. The results revealed filamentation of Psa after ST-F treatment, and fluorescence microscopy showed that ST-F inhibited the formation of the Z-ring composed of FtsZ protein. In vitro experiments and molecular docking demonstrated that ST-F can bind to FtsZ with a binding energy of 0.4 μM and inhibit FtsZ's GTP-dependent polymerization reaction. In addition, ST-F does not exert inhibitory effects on cell division in Psa strains overexpressing ftsZ. In conclusion, FtsZ is one of the target sites for ST-F inhibition of Psa, highlighting its potential as a therapeutic target for controlling Psa-induced kiwifruit bacterial canker.