Ricinus communis cyclophilin: functional characterisation of a sieve tube protein involved in protein folding

Abstract

The phloem translocation stream of the angiosperms contains a special population of proteins and RNA molecules which appear to be produced in the companion cells prior to being transported into the sieve tube system through the interconnecting plasmodesmata. During this process, these non-cell-autonomous proteins are thought to undergo partial unfolding. Recent mass spectroscopy studies identified peptidyl-prolyl cis-trans isomerase (PPIases) as potential molecular chaperones functioning in the phloem translocation stream (Giavalisco et al. 2006). In the present study, we describe the cloning and characterisation of a castor bean phloem cyclophilin, RcCYP1 that has high peptidyl-prolyl cis-trans isomerase activity. Equivalent enzymatic activity was detected with phloem sap or purified recombinant (His)(6)-tagged RcCYP1. Mass spectrometry analysis of proteolytic peptides, derived from a 22 kDa band in HPLC-fractionated phloem sap, immunolocalisation studies and Western analysis of proteins extracted from castor bean tissues/organs indicated that RcCYP1 is an abundant protein in the companion cell-sieve element complex. Microinjection experiments established that purified recombinant (His)(6)-RcCYP1 can interact with plasmodesmata to both induce an increase in size exclusion limit and mediate its own cell-to-cell trafficking. Collectively, these findings support the hypothesis that RcCYP1 plays a role in the refolding of non-cell-autonomous proteins after their entry into the phloem translocation stream.

FUNCTION OF PHLOEM-BORNE INFORMATION MACROMOLECULES IN INTEGRATING PLANT GROWTH & DEVELOPMENT

“…Microinjection experiments established that purified recombinant (His) 6-CYP1 can interact with PD to both induce an increase in SEL and mediate its own cell-to-cell trafficking. Collectively, these findings supported the hypothesis that this phloem CYP1 plays a role in the refolding of non-cell-autonomous proteins after their entry into the phloem translocation stream (Gottschalk et al 2008).…”

Master and servant: Regulation of auxin transporters by FKBPs and cyclophilins

“…The unusual FK506-binding domain in TWD1 was instead found to participate in protein interaction with ABCB-type auxin transporters and is apparently involved in the functional regulation of these transporters [44] (see Section 4). TWD1 also possesses a tetratricopeptide repeat domain (common [131] Regulation and PM-to-ER trafficking of ABCB-type auxin transporters [8,9] Z. mais [133] Interaction with ABCB transporters on PM (via FKB-domain) [8,62], ABCC transporters on tonoplast (via TPR domain) [66], with HSP90 (TPR domain) [62,65] and calmodulin (calmodulin-binding domain) [66] Over-expression of TWD1 lacking its membrane anchor results in hypermorphic growth [64] FKBP72/PAS1 A. thaliana [69] Unclear (C-terminal membrane anchor), nuclear [68,134] Low, inhibited by FK506 and rapamycin [134] Up-regulated cell division, leaf fusions, short hypocotyls, sterile [69] O. sativa [131] Chaperon during translocation of NAC-like transcription factor (AtFAN) into nucleus [68] Z. mais [133] Regulation of very long fatty acid elongation [70] -DGT/CypA/ROC1/CYP1/CYP2/ P. patens [10] Nuclear and cytoplasmic [10,90], phloem sieve elements [79] Significant [77,78], inhibited by CsA [78] Regulates growth [90], gene expression [84,90,92], patterned cell division [88], phloem function [79], ROS balance in root apical meristem [87] A. [137] in many large immunophilins) that was shown to interact with vacuolar ABC transporters of the C subclass and HSP90 [65,66], as w...…”

“…Arabidopsis ROC1, tomato DGT [78], Ricinus communis and rice CYCLOPHILIN1 [79]. Interestingly, similar to plant FKBPs, plant cyclophlins have been strongly linked to regulation of development (Box 2).…”

Plant Water Relations: Absorption, Transport and Control Mechanisms

“…Several HSPs -classified according to their molecular weight -are induced in conditions of water and saline stress, such as HSP70 (the DnaK family), the chaperones GroEL and HSP60, HSP90 and HSP100 and the small HSP (sHSP) (Alamillo et al, 1995;Campalans et al, 2001, Wang et al, 2004. Within these proteins, there is the cyclophilin, which is a chaperone protein with systemic properties and which is highly induced during water stress, conferring multiple tolerances to abiotic stress (Gottschalk et al, 2008;Sekhar et al, 2010). During conditions of stress, the recycling of macromolecules which lose their function to maintain cellular homeostasis is essential.…”