FKBP22 from the psychrophilic bacterium Shewanella sp. SIB1 selectively binds to the reduced state of insulin to prevent
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ORIGINAL PAPER
FKBP22 from the psychrophilic bacterium Shewanella sp. SIB1 selectively binds to the reduced state of insulin to prevent its aggregation Cahyo Budiman 1,2,3 & Carlmond Kah Wun Goh 3 & Irma Isnafia Arief 2 & Muhammad Yusuf 2 Received: 8 April 2020 / Revised: 8 November 2020 / Accepted: 17 November 2020 # Cell Stress Society International 2020
Abstract FKBP22 of a psychrophilic bacterium, Shewanella sp. SIB1 (SIB1 FKBP22), is a member of peptidyl-prolyl cis-trans isomerase (PPIase) and consists of N- and C-domains responsible for chaperone-like and PPIase catalytic activities, respectively. The chaperone-like activity of SIB1 FKBP22 was previously evidenced by its ability to prevent dithiothreitol (DTT)-induced insulin aggregation. Nevertheless, the mechanism by which this protein inhibits the aggregation remains unclear. To address this, the binding affinity of SIB1 FKBP22 to the native or reduced states of insulin was examined using surface plasmon resonance (SPR). The native and reduced states refer to insulin in the absence or DTT presence, respectively. The SPR sensorgram showed that SIB1 FKBP22 binds specifically to the reduced state of insulin, with a KD value of 37.31 ± 3.20 μM. This binding was facilitated by the N-domain, as indicated by the comparable KD values of the N-domain and SIB1 FKBP22. Meanwhile, the reduced state of insulin was found to have no affinity towards the C-domain. The KD value of SIB1 FKBP22 was slightly decreased by NaCl but was not severely affected by FK506, a specific FKBP inhibitor. Similarly, the prevention of DTT-induced aggregation by SIB1 FKBP22 was also modulated by the N-domain and was not affected by FK506. Further, the reduced and native states of insulin had no effect on the catalytic efficiency (kcat/KM) of SIB1 FKBP22 towards a peptide substrate. Nevertheless, the reduced state of insulin slightly reduced the catalytic efficiency towards refolding RNase T1, at up to 1.5-fold lower than in the absence of insulin. These results suggested that the binding event was mainly facilitated by hydrophobic interaction and was independent from its PPIase activity. Altogether, a possible mechanism by which SIB1 FKBP22 prevents DTT-induced insulin aggregation was proposed. Keywords FKBP . Psychrophilic . Chaperone . Peptidyl prolyl cis-trans isomerase (PPIase) . Surface plasmon resonance
Introduction A 22-kDa FK506-binding protein of a psychrophilic bacterium, Shewanella sp. SIB1 (SIB1 FKBP22), was assumed to be involved in the cold adaptation of this bacterium (Suzuki et al. 2004; Budiman et al. 2011). This protein belongs to peptidyl-
* Cahyo Budiman [email protected] 1
Department of Material and Life Science, Graduate School of Engineering, Osaka University, Yamadaoka, Suita 565-087, Japan
2
Department of Animal Production and Technology, IPB University, Indonesia, Jl Kampus IPB Darmaga, Bogor 16680, Indonesia
3
Biotechnology Research Institute, Universiti Malaysia Sabah, Jl UMS, 88400 Kota Kinabalu, Sabah, Malaysia
prolyl cis-trans isomerase (PPIase) famil
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