ABSTRACT
Mutations in the human creatine transporter 1 (CRT1/SLC6A8) cause the creatine transporter deficiency syndrome, which is characterized by intellectual disability, epilepsy, autism, and developmental delay. The vast majority of mutations cause protein misfolding and hence reduce cell surface expression. Hence, it is important to understand the molecular machinery supporting folding and export of CRT1 from the endoplasmic reticulum (ER). All other SLC6 members thus far investigated rely on a C-terminal motif for binding the COPII-component SEC24 to drive their ER export; their N-termini are dispensable. Here, we show that, in contrast, in CRT1 the C-terminal ER-export motif is cryptic and it is the N-terminus, which supports ER export. This conclusion is based on the following observations: (i) siRNA-induced depletion of individual SEC24 isoforms revealed that CRT1 relied on SEC24C for ER export. However, mutations of the C-terminal canonical ER-export motif of CRT1 did not impair its cell surface delivery. (ii) Nevertheless, the C-terminal motif of CRT1 was operational in a chimeric protein comprising the serotonin transporter (SERT/SLC6A4) and the C-terminus of CRT1. (iii) Tagging of the N-terminus-but not the C-terminus-with yellow fluorescent protein (YFP) resulted in ER retention. (iv) Serial truncations of the N-terminus showed that removal of ≥51 residues of CRT1 impaired surface delivery, because the truncated CRT1 were confined to the ER. (v) Mutation of P51 to alanine also reduced cell surface delivery of CRT1 and relieved its dependence on SEC24C. Thus, the ER-export motif in the N-terminus of CRT1 overrides the canonical C-terminal motif.
ABSTRACT
BACKGROUND: This study determined to what extent the underpinning of physiotherapeutic interventions with the evidence-based motivational psychological concept of the self-determination theory (SDT) by Ryan and Deci can increase motivation and enjoyment of movement in obese adolescents. METHODS: In this study 12 obese adolescents aged 14-18 years were offered a targeted group-specific sports program including a home exercise program of 8 weeks. The group leaders were trained in the SDT and supported to integrate motivational aspects. A SDT-based questionnaire by Kohake and Lehnert was used to evaluate motivational interventions. RESULTS: In total, seven (58%) patients finished the study. In the before-after comparison there were little changes in motivation. Results showed that contrary to expectations the motivation of the obese adolescents to move and to participate in the study was generally high. In the study, more internalized forms of motivation dominated, the highest quality form of motivation. CONCLUSION: Digital technologies could be a successful way to further increase motivation and compliance of our target group. This MotiMove study is a basis for future research programs and empower physiotherapists and movement experts to develop and implement training programs for obese adolescents and children.
