WBR0341

Author	[[PageAuthor::Rim Halaby, M.D. [1] (Reviewed by Yazan Daaboul, M.D. and Alison Leibowitz [2])]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Microbiology
Sub Category	SubCategory::Renal, SubCategory::General Principles
Prompt	[[Prompt::Human Immunodeficiency Virus (HIV) is a spherical retrovirus surrounded by an envelope composed of a phospholipid bilayer. It is a diploid virus composed of positive single-stranded RNA that codes for 9 viral genes. Two proteins on the surface of the viral envelope are derived from the env gene, which is essential for viral tropism. Which of the following proteins are required for viral attachment to host T-cell and entry, respectively?]]
Answer A	AnswerA::gp120 (attachment) and gp41 (entry)
Answer A Explanation	AnswerAExp::The HIV spike is composed of gp120, which is responsible for viral attachment to host CD4+ T-cell, and gp41, which is responsible for viral fusion and entry.
Answer B	AnswerB::gp41 (attachment) and gp120 (entry)
Answer B Explanation	AnswerBExp::In contrast, gp120 is responsible for viral attachment, and gp41 is responsible for viral fusion and entry.
Answer C	AnswerC::gp160 (attachment) and gp41 (entry)
Answer C Explanation	AnswerCExp::The cleavage of gp160, the protein product of the ''env'' gene, yields both gp120 and gp41.
Answer D	AnswerD::gp41 (attachment) and gp160 (entry)
Answer D Explanation	AnswerDExp::The cleavage of gp160, the protein product of the ''env'' gene, yields both gp120 and gp41.
Answer E	AnswerE::gp160 (attachment) and gp120 (entry)
Answer E Explanation	AnswerEExp::The cleavage of gp160, the protein product of the ''env'' gene, yields both gp120 and gp41.
Right Answer	RightAnswer::A
Explanation	[[Explanation::The HIV viral structure is an important determinant of tissue tropism. HIV infects a variety of immune cells by binding to either CCR5 or CXCR4. In order to infect these cells, both attachment and fusion/entry need to occur. The viral spike of the HIV virus, which is responsible for infection, is composed of 3 gp120 glycoproteins and 3 gp41 molecules that are non-covalently linked. Surface glycoproteins, gp120 and gp41, are derived from the cleavage of gp160, encoded by the env gene. The initial interaction between gp120 and CD4 leads to a conformational change, which exposes a new binding site for CCR5 or CXCR4. Induced by gp41, the subsequent conformational change results in the fusion of both membranes and the release of the viral capsid. Educational Objective: The HIV spike is composed of gp120, which responsible for viral attachment to host CD4+ T-cell and gp41, which is responsible for viral fusion and entry. References: Pancera M, Majeed S, Ban YE, et al. Structure of HIV-1 gp120 with gp41-interactive region reveals layered envelope architecture and basis of conformational mobility. Proc Natl Acad Sci USA. 2010;107(3):1166-71. First Aid 2014 page 167]]
Approved	Approved::Yes
Keyword	WBRKeyword::HIV, WBRKeyword::Attachment, WBRKeyword::Entry, WBRKeyword::Viral proteins, WBRKeyword::Proteins, WBRKeyword::Gp120, WBRKeyword::Gp41, WBRKeyword::Gp160, WBRKeyword::Fusion, WBRKeyword::Retrovirus, WBRKeyword::Virus
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::