Folding, Modification, and Degradat

Folding, Modification, and Degradation of Proteins
■ The amino acid sequence of a protein dictates its folding into a specific three-dimensional conformation, the native state.
■ Protein folding in vivo occurs with assistance from molecular chaperones (Hsp70 proteins), which bind to nascent polypeptides emerging from ribosomes and prevent their misfolding (see Figure 3-11). Chaperonins, large complexes of Hsp60-like proteins, shelter some partly folded or misfolded proteins in a barrel-like cavity, providing additional time for proper folding.
■ Subsequent to their synthesis, most proteins are modified by the addition of various chemical groups to amino acid residues. These modifications, which alter protein
structure and function, include acetylation, hydroxylation, glycosylation, and phosphorylation.
■ The life span of intracellular proteins is largely determined by their susceptibility to proteolytic degradation by various pathways.
■ Viral proteins produced within infected cells, normal cytosolic proteins, and misfolded proteins are marked for destruction by the covalent addition of a polyubiquitin chain and then degraded within proteasomes, large cylindrical complexes with multiple proteases in their interiors generative diseases are caused by aggregates of proteins that are stably folded in an alternative conformation

Hasil (Bahasa Indonesia) 2:

Lipat, Modifikasi, dan Degradasi Protein
■ Urutan asam amino dari protein menentukan lipat ke dalam konformasi tiga-dimensi tertentu, negara asli.
■ Protein lipat in vivo terjadi dengan bantuan dari pendamping molekul (protein Hsp70), yang mengikat polipeptida baru lahir muncul dari ribosom dan mencegah misfolding mereka (lihat Gambar 3-11). Chaperonins, kompleks besar protein Hsp60-seperti, berlindung beberapa protein sebagian dilipat atau gagal melipat di rongga barel-seperti, memberikan waktu tambahan untuk lipat yang tepat.
■ Setelah sintesis mereka, kebanyakan protein dimodifikasi dengan penambahan berbagai kelompok kimia untuk amino residu asam. Modifikasi ini, yang mengubah protein
struktur dan fungsi, termasuk asetilasi, hidroksilasi, glikosilasi, dan fosforilasi.
■ Rentang hidup protein intraseluler sangat ditentukan oleh kerentanan mereka terhadap proteolitik degradasi oleh berbagai jalur.
■ protein virus yang diproduksi di dalam sel yang terinfeksi, sitosol yang normal protein, dan protein yang gagal melipat ditandai untuk kehancuran dengan penambahan kovalen dari rantai polyubiquitin dan kemudian terdegradasi dalam proteasomes, kompleks silinder besar dengan beberapa protease di interior mereka penyakit generatif disebabkan oleh agregat protein yang stabil dilipat dalam konformasi alternatif