title: Indian hedgehog mutations causing brachydactyly type A1 impair Hedgehog signal transduction at multiple levels.
abstract: Brachydactyly type A1 (BDA1), the first recorded Mendelian autosomal dominant disorder in humans, is characterized by a shortening or absence of the middle phalanges. Heterozygous missense mutations in the Indian Hedgehog (IHH) gene have been identified as a cause of BDA1; however, the biochemical consequences of these mutations are unclear. In this paper, we analyzed three BDA1 mutations (E95K, D100E, and E131K) in the N-terminal fragment of Indian Hedgehog (IhhN). Structural analysis showed that the E95K mutation changes a negatively charged area to a positively charged area in a calcium-binding groove, and that the D100E mutation changes the local tertiary structure. Furthermore, we showed that the E95K and D100E mutations led to a temperature-sensitive and calcium-dependent instability of IhhN, which might contribute to an enhanced intracellular degradation of the mutant proteins via the lysosome. Notably, all three mutations affected Hh binding to the receptor Patched1 (PTC1), reducing its capacity to induce cellular differentiation. We propose that these are common features of the mutations that cause BDA1, affecting the Hh tertiary structure, intracellular fate, binding to the receptor/partners, and binding to extracellular components. The combination of these features alters signaling capacity and range, but the impact is likely to be variable and mutation-dependent. The potential variation in the signaling range is characterized by an enhanced interaction with heparan sulfate for IHH with the E95K mutation, but not the E131K mutation. Taken together, our results suggest that these IHH mutations affect Hh signaling at multiple levels, causing abnormal bone development and abnormal digit formation.
authors.affiliation: Bio-X Center, Key Laboratory for the Genetics of Developmental and Neuropsychiatric Disorders (Ministry of Education), Shanghai Jiao Tong University, Shanghai 200030, China.
authors.forename: Gang
authors.initials: G
authors.lastname: Ma
authors.forename: Jiang
authors.initials: J
authors.lastname: Yu
authors.forename: Yue
authors.initials: Y
authors.lastname: Xiao
authors.forename: Danny
authors.initials: D
authors.lastname: Chan
authors.forename: Bo
authors.initials: B
authors.lastname: Gao
authors.forename: Jianxin
authors.initials: J
authors.lastname: Hu
authors.forename: Yongxing
authors.initials: Y
authors.lastname: He
authors.forename: Shengzhen
authors.initials: S
authors.lastname: Guo
authors.forename: Jian
authors.initials: J
authors.lastname: Zhou
authors.forename: Lingling
authors.initials: L
authors.lastname: Zhang
authors.forename: Linghan
authors.initials: L
authors.lastname: Gao
authors.forename: Wenjuan
authors.initials: W
authors.lastname: Zhang
authors.forename: Yan
authors.initials: Y
authors.lastname: Kang
authors.forename: Kathryn S E
authors.initials: KS
authors.lastname: Cheah
authors.forename: Guoyin
authors.initials: G
authors.lastname: Feng
authors.forename: Xizhi
authors.initials: X
authors.lastname: Guo
authors.forename: Yujiong
authors.initials: Y
authors.lastname: Wang
authors.forename: Cong-zhao
authors.initials: CZ
authors.lastname: Zhou
authors.forename: Lin
authors.initials: L
authors.lastname: He
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D059327:Brachydactyly / Q000235:genetics* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D018360:Crystallography, X-Ray; D053823:Hedgehog Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D006493:Heparin / Q000737:chemistry / Q000378:metabolism; D006579:Heterozygote; D006801:Humans; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D000072079:Patched Receptors; D000072081:Patched-1 Receptor; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011956:Receptors, Cell Surface / Q000378:metabolism; D015398:Signal Transduction; D013696:Temperature
chemical_list: D053823:Hedgehog Proteins; C000606236:PTCH1 protein, human; D000072079:Patched Receptors; D000072081:Patched-1 Receptor; D011956:Receptors, Cell Surface; D006493:Heparin; D002118:Calcium