WBR0341

Author	[[PageAuthor::Rim Halaby, M.D. [1], Alison Leibowitz [2] (Reviewed by Alison Leibowitz)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Microbiology
Sub Category	SubCategory::Renal, SubCategory::General Principles
Prompt	[[Prompt::Human Immunodeficiency Virus (HIV), unique in structure when compared to other retroviruses, is spherical with a diameter of approximately 120 nm, surrounded by a viral envelope composed of a phospholipid bilayer, which forms when the virion buds from the infected cell. HIV is a diploid virus composed of positive single-stranded RNA, coding 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 represent the protein required for viral attachment and entry, respectively?]]
Answer A	AnswerA::gp120, gp41
Answer A Explanation	AnswerAExp::The HIV spike is composed of gp120, responsible for viral attachment and gp41, responsible for viral fusion.
Answer B	AnswerB::gp41, gp120
Answer B Explanation	AnswerBExp::Contrarily, gp120 is responsible for viral attachment and gp41 is responsible for viral fusion.
Answer C	AnswerC::gp160, gp41
Answer C Explanation	AnswerCExp::The cleavage of gp160, the protein product of the env gene, yields both gp120 and gp41.
Answer D	AnswerD::gp41, gp160
Answer D Explanation	AnswerDExp::The cleavage of gp160, the protein product of the env gene, yields both gp120 and gp41.
Answer E	AnswerE::gp160, gp120
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, 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 in gp41, the subsequent conformational change, termed entry, results in the fusion of both membranes and the release of the viral capsid. Educational Objective: The HIV spike is composed of gp120, responsible for viral attachment and gp41, responsible for viral fusion. 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.]]
Approved	Approved::Yes
Keyword	WBRKeyword::HIV, WBRKeyword::attachement, WBRKeyword::viral fusion, WBRKeyword::gp120, WBRKeyword::gp41, WBRKeyword::immune system, WBRKeyword::env gene
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::