WBR0341

Author	[[PageAuthor::Rim Halaby, M.D. [1]]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Microbiology
Sub Category	SubCategory::Renal, SubCategory::General Principles
Prompt	[[Prompt::The HIV virus is unique in structure compared to other retroviruses. It is spherical with a diameter of approximately 120 nm, surrounded by a viral envelope composed of a phospholipid bilayer formed when the virion buds from the infected cell. It is a diploid virus composed of positive single-stranded RNA coding for 9 viral genes. On the surface of the viral envelope are 2 proteins derived from the env gene essential for viral tropism. Which of the following represent the protein required for viral attachement 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::The opposite is correct, gp120 is responsible for viral attachment and gp41 is responsible for viral fusion.
Answer C	AnswerC::gp160, gp41
Answer C Explanation	AnswerCExp::gp160 is the protein product of the ''env'' gene and its cleavage yields both gp120 and gp41.
Answer D	AnswerD::gp41, gp160
Answer D Explanation	AnswerDExp::gp160 is the protein product of the ''env'' gene and its cleavage yields both gp120 and gp41.
Answer E	AnswerE::gp160, gp120
Answer E Explanation	AnswerEExp::gp160 is the protein product of the ''env'' gene and its cleavage yields both gp120 and gp41.
Right Answer	RightAnswer::A
Explanation	[[Explanation::The HIV viral structure is an important determinant of tissue tropism. The HIV virus infects a variety of immune cells by binding 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 is responsible for this function. It is composed of 3 gp120 glycoproteins and 3 gp41 molecules that are non-covalently linked. gp120 and gp41 are the derived from the cleavage of gp160 the protein product of the env gene. The initial interaction between gp120 and both CD4 and CCR5 is termed attachment. The subsequent conformational changed induced in gp41 causing the fusion of both membranes and release of the viral capsid is termed entry. Both of these mechanisms are essential for viral pathogenesis. Educational objective: The HIV spike is composed of gp120 responsible for viral attachment and gp41 responsible for viral fusion. Reference: 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. Educational Objective: References: ]]
Approved	Approved::No
Keyword	WBRKeyword::HIV, WBRKeyword::attachement, WBRKeyword::entry, WBRKeyword::gp120, WBRKeyword::gp41
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::