Two novel mutations in the bestrophin-1 gene and associated clinical observations in patients with best vitelliform macular dystrophy

Bestrophin proteins are calcium (Ca2+)-activated chloride channels. Mutations in bestrophin 1 (BEST1) cause macular degenerative disorders. Whole-cell recordings show that ionic currents through BEST1 run down over time, but it is unclear whether this behavior is intrinsic to the channel or the result of cellular factors. Here, using planar lipid bilayer recordings of purified BEST1, we show that current rundown is an inherent property of the channel that can now be characterized as inactivation. Inactivation depends on the cytosolic concentration of Ca2+, such that higher concentrations stimulate inactivation. We identify a C-terminal inactivation peptide that is necessary for inactivation and dynamically interacts with a receptor site on the channel. Alterations of the peptide or its receptor dramatically reduce inactivation. Unlike inactivation peptides of voltage-gated channels that bind within the ion pore, the receptor for the inactivation peptide is on the cytosolic surface of the channel and separated from the pore. Biochemical, structural, and electrophysiological analyses indicate that binding of the peptide to its receptor promotes inactivation, whereas dissociation prevents it. Using additional mutational studies we find that the “neck” constriction of the pore, which we have previously shown to act as the Ca2+-dependent activation gate, also functions as the inactivation gate. Our results indicate that unlike a ball-and-chain inactivation mechanism involving physical occlusion of the pore, inactivation in BEST1 occurs through an allosteric mechanism wherein binding of a peptide to a surface-exposed receptor controls a structurally distant gate.

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“…3 C). Notably, the mutation of W229 to glycine has been identified in patients with Best vitelliform macular dystrophy (Lin et al, 2015).…”

Section: Resultsmentioning

confidence: 99%

An allosteric mechanism of inactivation in the calcium-dependent chloride channel BEST1

Vaisey

Long

2018

Journal of General Physiology

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“…Bestrophin-1 is the product of the gene BEST1. This protein is mainly expressed in the basolateral plasma membrane of the RPE ( 19 ). This protein contains several domains with a high degree of evolutionary conservation.…”

Section: Discussionmentioning

confidence: 99%

Two heterozygous mutations identified in one Chinese patient with bilateral macular coloboma

Gao

Chen

et al. 2017

Molecular Medicine Reports

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Congenital macular coloboma is characterized by defined punched out atrophic lesions of the macula. The present study aimed to investigate the genetic alterations of one Chinese sporadic patient with bilateral large macular coloboma. Complete ophthalmic examinations, including best-corrected visual acuity, slit-lamp examination, fundus examination, fundus photograph and fundus fluorescein angiography imaging, Pentacam, and optical coherence tomography were performed on the patient. Genomic DNA was extracted from leukocytes in a peripheral blood sample collected from the patient, the patient's unaffected family members and from 200 unrelated control subjects from the same population. Next-generation sequencing of the known genes involved in ocular disease was performed. The functional effects of the mutation were analyzed using Polymorphism Phenotyping (PolyPhen) and Sorting Intolerant From Tolerant (SIFT). One heterozygous bestrophin 1 (BEST1) mutation c.1037C>A (p.Pro346His, p.P346H) in exon 9 and one heterozygous regulating synaptic membrane exocytosis 1 (RIMS1) mutation c.3481A>G (p.Arg1161Gly, p.R1161G) in exon 23 were identified in the patient being investigated, but not in the unaffected family members or unrelated control subjects. Polyphen and SIFT predicted that the amino acid substitution p.P346H in the BEST1 protein is damaging. In addition, Polyphen predicted that the amino acid substitution p.R1161G in the RIM1 protein is damaging. The results of the current study have increased the mutation spectrums of BEST1 and RIMS1, and are valuable for improving the current genetic counseling process and developing novel therapeutic interventions for patients with macular coloboma.

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“…However, several extramacular lesions were also present. Hyperopia greater than +3.00 diopters is a recognized feature of juvenile-onset BVMD ( 31 , 40 ). In this study, Patient 1 exhibited hyperopia, whereas Patient 2 exhibited myopia.…”

Section: Discussionmentioning

confidence: 99%

“…Genomic DNA was extracted from peripheral blood leucocytes using a DNA extraction kit (Qiagen GmbH, Hilden, Germany) ( 29 , 30 ). Exons of the BEST1 gene were amplified by polymerase chain reaction (PCR) with primers as previously described ( 31 – 34 ). The primer sequences are listed in Table I .…”

Section: Methodsmentioning

confidence: 99%

Genetic variations in Bestrophin‑1 and associated clinical findings in two Chinese patients with juvenile‑onset and adult‑onset best vitelliform macular dystrophy

Gao

et al. 2017

Mol Med Report

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Best vitelliform macular dystrophy (BVMD) is a hereditary retinal disease characterized by the bilateral accumulation of large egg yolk-like lesions in the sub-retinal and sub-retinal pigment epithelium spaces. Macular degeneration in BVMD can begin in childhood or adulthood. The variation in the age of onset is not clearly understood. The present study characterized the clinical characteristics of two Chinese patients with either juvenile-onset BVMD or adult-onset BVMD and investigated the underlying genetic variations. A 16-year-old male (Patient 1) was diagnosed with juvenile-onset BVMD and a 43-year-old female (Patient 2) was diagnosed with adult-onset BVMD. Comprehensive ophthalmic examinations were performed, including best-corrected visual acuity, intraocular pressure, slit-lamp examination, fundus photography, optical coherence tomography, fundus fluorescein angiography imaging and Espion electrophysiology. Genomic DNA was extracted from peripheral blood leukocytes collected from these patients, their family members, and 200 unrelated subjects within in the same population. The 11 exons of the bestrophin-1 (BEST1) gene were amplified by polymerase chain reaction and directly sequenced. Both patients presented lesions in the macular area. In Patient 1, a heterozygous mutation c.903T>G (p.D301E) in exon 8 of the BEST1 gene was identified. This mutation was not present in any of the unaffected family members or the normal controls. Polymorphism phenotyping and the sorting intolerant from tolerant algorithm predicted that the amino acid substitution D301E in bestrophin-1 protein was damaging. In Patient 2, a single nucleotide polymorphism c.1608C>T (p.T536T) in exon 10 of the BEST1 gene was identified. These findings expand the spectrum of BEST1 genetic variation and will be valuable for genetic counseling and the development of therapeutic interventions for patients with BVMD.

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Two novel mutations in the bestrophin-1 gene and associated clinical observations in patients with best vitelliform macular dystrophy

Cited by 9 publications

References 22 publications

An allosteric mechanism of inactivation in the calcium-dependent chloride channel BEST1

An allosteric mechanism of inactivation in the calcium-dependent chloride channel BEST1

Two heterozygous mutations identified in one Chinese patient with bilateral macular coloboma

Genetic variations in Bestrophin‑1 and associated clinical findings in two Chinese patients with juvenile‑onset and adult‑onset best vitelliform macular dystrophy

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